Everything you would want to know about Map Projections!

all right so today we're going to be talking about map projections and coordinate systems and these fall under a general field of study called geodesy or studying the size in the shape of the earth and so this is one of the things that probably ESRI and with arcmap and GIS it does the best that is that it does a very good job you working with multiple projections at coordinate systems just to quickly understand Giada's he I'm going to show you a quick video from NASA long time ago in ancient Egypt the clever human named Eratosthenes figured out that when the Sun was directly above a deep well in one city you could stand in a nearby city to the north and measure the angle of the shadows there and multiply that by the distance between the two cities to get the distance around the entire earth with that the science of geodesy was born G Odyssey deals with the measurement and representation of the earth or to put it more simply it's the science of where things are and just as importantly where they have been and where they are going through geodesy we learned the rough size and shape of the earth the direction of its rotation its distance from the Sun and more through triangulation we could create detailed maps of entire countries we even figured out that the earth isn't quite a perfect sphere and after some arguments and expeditions to Lapland and Peru we measured that it's just a bit thicker in the middle building on this information we found tons of practical uses for geodesy using stars as reference points and accurate watches we could reliably determine latitude and longitude so that ships could cross giant oceans to get where they needed to go explorers visited uncharted regions mapped them and even found the tallest mountain in the world later engineers built railroads to get us to all of these places with a little math in the same reference surface rail tunnels could be started on both sides of a mountain and somehow still meet in the mill life was good and once we invented radio telescopes and satellites things got even better when scientists used a bunch of small radio dishes like one big one to look at quasars somebody got the idea that you could use these measurements to determine very accurately the distance between the telescopes now we can look at the movement of the Earth's crust change and how long days are and how the earth wobbles on its axis satellites also became very important by analyzing their orbits we can learn about our planets changing size and shape and gravity and by making laser measurements we can look at everything from changes in the height and shape of the oceans and ice sheets to how the tides work so from ancient Egypt to the hundreds of satellites in orbit today G Odyssey continues to add a huge impact on our lives and all because somebody a long time ago decided to look down a well so that quick overview just quickly goes from all ideas of coordinate systems and geodesy in general from beginning to the end but now we're gonna like really get you know where the rubber hits the road learned a lot of terminology and learned actually how we use all these things in photography and in GIS and so if you look here and it's a list of terminology that maybe you should get familiar with we're gonna talk we're gonna say these terms throughout the the lecture but there's no reason to go over them right now but just keep these terms in mind as you are looking through the lecture so whenever you look at the earth this is I guess the simplest way to project the earth onto a 2d surface whenever you look at the earth and it's a 3d object and you want to put into 2d you can there's a lot of different ways of doing it and the easiest way is just to take a picture basically at the earth take a photo of the earth and say okay I'm done I made my map and so you know this is you know you start thinking about what kind of problems what we have if maps were made this way and one major problem that comes up is that you only see half the earth there's the other side of the planet and so you know at minimum you would have to have two shots to get a global view but then there's other issues that happen with it with this kind of projection as well and because things start getting distorted around the very edges of the of the planet you also have problems you can't make measurements the only place that makes good measurements is from the center looking out where's measuring distances or angles but everything else doesn't make good measurements and so there's a lot of problems with this kind of flat projection like this and so you have to start looking at other ways of making projections of the earth and so the goal of projecting the earth is to take a 3d object to earth and make it into a 2d object a piece of map and we want to portray the earth on those flat surfaces but the problem is whenever we do that we're going to be getting distortion and we'll always have some kind of distortions either scales areas directions or angles mathematical scale solves the size problem but getting rid of distortion is another mathematical challenge so here's the problem what we professional cartographers referred to as the orange peel problem you want a map what's on the outside of it onto a piece of flat paper if you take the skin of the earth off it and put it down on the ground it's not flat it isn't a flat thing I mean as much as you try to flatten it it it kind of sticks up and this is the problem that all cartographers have to deal with all people who make maps it's a basic geometry problem over thousands of years photographers have devised clever formulas that describe how points from one surface can be transferred to another some project these points onto a cylinder others project they wanna cone still others project points directly to the plane but there is no perfect way to flatten the earth every projection has some Distortion [Music] a famous example is a map made by Gerardo's Makeda in 1569 any line drawn across it was show a constant compass direction and for centuries sailors used it to chart courses around the world merket has become synonymous with map Mercator equals map most school rooms had Mercator projections in them people even knew the name Mercator means a famous person an example of the huge distortion on Mercator maps is shown here with Greenland Greenland is actually the size of Mexico and you can see how enormous it's got here because of the distortion of the particular projection that was never meant to show the relative sizes of the countries was meant as a navigational tool there are all sorts of maps some good some bad some quirky but all of these start from somebody measuring something the way you represent that measurement that mathematical measurement can take so many different forms that the scope of the word map is enormous [Music] so yeah so this is like the basic problem that we're having we're trying to flatten the earth and so we have this you know globe that's in it's a you know that's what we live on a 3d globe and the problem is is that whenever we want to take that you know that information with us and you know put it for example in our pocket or something and go to the field or do a hike or something we can't really work with carrying around Globes we're gonna be having problems so we have to somehow take this 3d object and put it on to 2d and whenever we do that there's a few different ways of doing it either having will go over those in a second but whenever we do those whenever we make that thing into 3d we always have distortions so we have to start trying to engineer what's the best projection for our project and wait to decide okay what are we trying to represent what are we trying to do with this map what do we need to minimize the distortions in is it in distance or is it directions or scale or area and so that's stuff to keep in mind so if we go to that orange pill problem this is the classic problem here taking the orange pill but it's it's funny because a lot of these projections whenever you play with the orange peel you actually can find projections that have done that and so there are projections out there that are just basically peeling oranges but the issue happens then is that you have these situations here where you have these kind of cuts you know so you can't really measure between those two things you can try to be strategic in your cuts and put them in oceans but then you know you have poor things like Greenland here getting cut and have or cut in pieces so they're adding it on both sides and so this is you know not a very practical way to make to make a map there's also you know trying to be more strategic like this and make these cuts in the maps in the past have done to have done things like this but the best projections are gonna have distortions and so you're going to try to fit it onto a you know a square for example or a sorry a rectangle and and have a completely fill up the whole page and so you guys started thinking about how am I gonna do these projections and so whenever you look at projections there's a few different ways to doing this there's the spherical method or ellipsoidal method depends on what model the earth you're using ellipsoid or spherical and then whenever you have that the that kind definition of the earth then you can either project what's on there onto a flat plane or you can project it project it onto a cylinder or onto a cone and so that's kind of like how the three major things are so it's a plane cylinder or cone but the truth is is that you can have infinite numbers varieties of flat surfaces you can have poly conics for example that are multiple cones put together so these are things to keep in mind about especially with computing powers that you can have a lot more options available to you whenever whenever we want to take a projection though so say we want to make a map and we say okay we'll use this projection some of the first things we think about is what is our geodetic datum what is the model of the earth that we're going to be using and this is what's gonna define the size and shapes of the earth it's also give us our reference ellipsoid so exactly the you know how much wider or taller the earth days it defines ledged longitudinal and latitude for the coordinate system and there's other things in datums and different constraints like the gravitational fields and so forth that are also that could also be used and so the typical datums that people think of at first our stuff like the world geodetic datum of us our weird world geodetic surveying 1984 or North American datum 1983 and these are just definitions of you know of course the size of shapes of Earth but also the longitude latitudes and so just quickly to to think about longitude latitude there's two main lines of it remember the equator which is degrees latitude which is going to be equal distance from the north to the South Pole and then the Prime Meridian which is politically set at Greenwich England a zero degrees longitude and so we have here the two kind of you know the zero zeros and where those two places meet we call that null island that's where a lot of GIS mishaps happen off the coast of Africa because if you have projection issues you're gonna end up with your data hanging out in a null Island and so let's talk about the sphere so is the world a sphere so a lot of people will say oh yeah of course the world's world is is this here so it's a it's a it's round like a ball and like here you go it has equal radius from the center of the earth and the problem is is that that's not true so the earth is not this here so what it's not round not sound like a flat earther huh so no the truth is the earth is round but it's not round like a sphere and as you can see here know the Flat Earth Society for people don't know about it it's there's a kind of like an organization here it's kind of like we can call them like the original deniers and you can see here a flower society's website it's I think is more of a gag but there's in in the past and really ancient times people thought that the earth might be flat but you know you saw from the geodesy video that that's been kind of debunked a long time ago but um so it's not flat and it's not round like a ball so no what is it and so does anyone know what it is well yeah we figured it out and it's not round like a ball it's round like a spheroid or an ellipsoid so you can see here the what's going on with the earth is that it's a little bit shorter because this red represents a perfect circle and it's a little bit fatter so it's a little shorter and fatter then it's supposed to be and you can see here the distance if we measure distance around the Earth from the from the pole to pole it's gonna be forty thousand and seven kilometers but then whenever he measure it around the equator it's forty thousand seventy four kilometers so that's quite you know quite a big difference in circumference across those two those two values and so why is this happening you know we have this video here it gets kind of loud but this was something I was going on on YouTube and stuff where people were hooking themselves up to office chairs with leaf blowers but you can see here I could easily use a ballerina but this is a little bit more fun but you can see here what's going on with a guy he's spinning around in a circle using his leaf blower to go faster and faster I want you to pay attention to the sinner at the his gravity over there where he's spinning and he's trying to keep himself in his chair as much as he can but there's something pulling him out something that doesn't allow him to do that and his legs end up popping out bolla and that's that's kind of what's happening the earth the earth spinning around in a circle and the sinner of this the axes wordsworth spinning that center of mass they're starting to bulge out because of its spin and that's what makes makes the earth little bit chunkier and in the middle this is known as the centrifugal force which is just a because bodies and motions kind of stay in motion so you get this kind of inertia that happens across the center of the earth because it's a little bit further out from the spin so it's actually having more inertia forces impacting it and it's causing it's kind of how that centrifugal force push out on the on the on the rotating body from the center and so that's what's happening to the earth and so what ends up being a better definition of the earth is an ellipsoid which is what we have here which is basically looks like a ball like a sphere but it's just a little bit.you one of the axes are shorter than the other axes so it's more like yet an ellipse I supposed to rotate a circle across an axes to make a sphere you're gonna rotate an ellipse around this to make ellipse and so on ellipsoids gonna have a few different parameters you're gonna have your semi minor axis which is gonna be your your smaller of the two radii and so this is what's going on here from this center of the earth to the pole and then you never semi-major axes over here from the Senate earth to the equator and so whenever you put those numbers in you start creating your geodetic datum and if you say okay I'm going to use an ellipsoid that's in define the shape of the earth and you're gonna put on top of it a coordinate system and then you're ready to go with your GIS a lot of people take this for granted because we're always working with earth but whenever you start looking at other planets say you're gonna do some mapping of the moon or mapping of Mars I see a lot of people use actually GIS to do those things then you start messing with these numbers here to debride to find the size of shape or luckily in GIS a lot of times we're going to be using definitions that already exist through the either the world geodetic survey 1984 not a North American datum 1983 those are the two that I would say are the probably the best out there but if you're working with maps before 1984 or 1983 you're going to start looking at what datums did they use in longitude latitude actually was different over time because of that so you can actually actually have small variations in your longitude latitude one thing to keep in mind is that Mo's longitude latitude today is being assumed to be working with GPS and so that's going to be working with nad 84 because sorry wgs84 the world geodetic survey 1984 because that's the the native datum for for GPS it is also worth mentioning geoids here so we talked about taking geometric shapes and kind of making them try to fit the best as we can as Earth geoids are interesting because they don't take geometric shapes they take some kind of earth property and use that to define the size and shape of Earth so like here for example in this image you're taking the taking constant value of gravity and using that to define this the size shape they're going to be the best this is exaggerated this is why those shapes like this by the way but this is a better way of doing mapping what the problem is it's kind of not intuitive as we are used to and it takes a lot of computational power so in the future one day we'll be using geoids because we'll just use computers to do everything and the computers will work better with will it's better to have accuracy so why a man over the care about the computation power so we use geoids today we're using you know ellipsoids and we're laughing at people in the past to use fear as spheres to map the earth and so one day our you know next few generations they'll be laughing at us for using the lope sites but enjoy is again a mathematical figure or the earth but what it's going to end up using is it and try to find some kind of earth property and typically that earth property is a gravitational measurement that's usually the best one out there so if you compare these two things to each other here is an ellipsoid surface but on the in the red dots and you can see here that's the perfect kind of like a lip soit smooth lips wait but then the others geoid here in the blue line that's actually changing because of topographic topographic masses because actually whenever you have a topographic mass like something like a mountain or something you get small changes in what's happening with the Earth's gravitational constant because of those huge masses of Earth and so what happens to the size and shape of the earth so if we look here we've had actually so many different variations here's the equatorial radii of the other earth on different kinds of definitions look at these just different different definitions out there we can see that we got the few first few numbers right but look at these last numbers I mean they're jumping around from 245 388 all the way up here into the 70s where we start getting into the 135 so basically until 1979 1984 we've just been having all these different numbers popping around and so now we figured it out alright so Wow great we figured out 1984 we figured out that the earth is what size of Earth days and so this is a little joke I'd like to make you know how did we figure that out before we even put a man on the moon so you know if we want to go with the Flat Earth deniers you say here moon-landing deniers too but the truth is the space race is what helped us find out the the size and shape of the earth because whenever we did the space race we also started putting lots of satellites up into space and those satellites helped us with the measurement and the size and shape to the earth and so then afterwards we were able to get really good measurements and then even we were able to put up a world you world global positioning system which is all satellite based to up there and so this is why this is how we were able to figure it out so the space race is to thank for that so the three basic projections so now that's all datum so we figured out how we defined the size and shape of Earth now we're going to talk about how we take that 3d objects into a 2d objects and so here we have the cylindrical conical and planar projections and so basically we're taking this shape and we're putting it around the Earth and then we're projecting outwards in this case outwards on to the shape and C and so outwards onto the shape and so this 3d object is being projected here so like if you have a cylindrical projection here where the the cylinder is touching the earth there's like almost no distance that projection has to travel to transfer it onto the earth on to the cylinder but when you're starting up to the poles look at this that distance that has to travel that becomes just pure distortion and so this is the problem that happens here is that as you further get away from the equator that cylinder projection is going to be completely distorted we can use conical projections to kind of solve some of those problems for regional areas but you can see here of course you're gonna have big big distortions as you get further across the cone and then plane our projections of course are gonna be used for only special cases and so whenever we look at those projections and we start saying okay what's the most famous with a cinder cone projection that's the Mercator projection so here's the Mercator projection here we can see they just cut off the North and the South Pole because what's happening it's goes to infinity it becomes infinite at the poles is completely Distortion and so there's a point where you just say you know what we're just tired of the distortion if you look here at the Lambert conformal conic that's gonna be the most famous conical projection and these are usually used for these kind of continental this would be the best way to represent the the the North it's a North American continent and then you also have here the Lambert asthma as mu whole equal area projection and this is a projection here as a planar projection so these are like the three kind of famous ones if you wanted to look him up one thing that was one thing that was kind of figured out by smart Katara first somewhere I can't I don't know exactly the origins of this but this is something that is very useful so here's the typical cynical projection you put the earth on the you put the cylinder on top of the earth and you have it touching likeness say for example out the equator and then everything north or south of the Equator is going to be distorted based off of the distance that is traveled from the earth to get to the projected surface the only place you have a one-to-one scale is here and then after you keep going up and up to scale just keeps key and exaggerated so someone thought well you know what why not this actually go through the earth this have this under go through the earth and then we project the equatorial regions downwards towards the subjection surface and then the area's above these these sequence outwards towards the projection so you can see how that's going on so what this does that's very interesting is that it takes this distortion here that would have happened at the very northern poles for example and greatly reduces it and redistributes it to discern the earth so what ends up having L equal to 1 but you also have these areas in the middle that are distorted a little bit a little bit exaggerated and then these areas over here I mean a little bit the opposite of exaggerated like minimized and then over here these areas will be exaggerated so here would be shrunk and never be exaggerated but overall the absolute scale error will be less with this and that's what's really great about the secant projections and so whenever you look at some projections hypes is a syndrome called projection conical and planar those are the three remember and so here's their tie here's what they're good for so cynical projections we're good for global displays that's what people like to use them for what they're really nice about it that the straight meridians and parallels so those things are straight so them becomes kind of like graph paper but the big problem with them is that you get large area distortions the conical projections you lose the straight midians aperio parallels but now you have areas proportional to each other and you also have local direction as true and then of course you have the planar planar projection which you lose half the earth to like at the beginning we were talking about the very beginning but you also get here distances from the origins are true and so these are actually good for in some particular cases so what's the appropriate projections that we should use for global display my favorites Robinson projection it does a pretty good job at you know showing the whole world but it doesn't really do other things good but at least this is something it's a better version of Mercator there's Lambert conformal conic which are good for regional shapes so if you start your regional mapping on global mapping the LCCC lambert conformal conic is good for things that are longer east to west so I want you to think about things like Tennessee that kind of the Tennessee state lines that would be some that would be good to be represented with the glamper conformal conic a transverse Mercator though on the other hand is going to be good for regional shapes that are good north-south think about California for transverse Mercator that's what they're going to do that's way going to be good for and so here's a pig here is a map in Robinson projection so you can see Robinson projection does a great job representing the whole world but is it perfect it's not perfect of course it has a lot of it like for example these lines are not straight the areas themselves aren't perfectly preserved but it does a good job doing the whole world at once it's way better than then Google sorry way better than Mercator so I wanted to look at this web Mercator a web app here that's pretty nice at showing distortions of the different countries of the world and so if you start looking at countries near the equatorial point at the equator you're gonna start finding major distortions so for example here we have Morocco so if I put Morocco here where it belongs you get kind of this distortion that happens here if I bring it to the center this is maybe close this is actually closer to what the actual size is you can see how you start getting smaller distortions here what if I move it towards Greenland so you can see how Greenland is actually being majorly exaggerated what if I move it towards Norway in Sweden look at Scandinavia look at places in Europe so while these countries in the equatorial regions may seem like they're kind of like smaller just because of the fact that they the projections that happen here make them seem smaller I'm going to refresh this here because I want to find one that has Mexico so here's Mexico and so this is the example that was from the video whenever you take Mexico to Greenland and so you can see here that Greenland and Mexico are fairly similar in size within the course because of the Mercator projection you get this kind of distortion that happens so here's Greenland and you're not here in Mexico similar slices look at it it's I mean you said it's a good size but is it this big and you can see how you get closer to the North Pole even though more exaggerated things become this is actually what you can start thinking about what happens to Antarctica here look at what goes on over here it just starts taking over everything that's because of the fact that it's just being completely exaggerated there at the poles so I'm going to drop Greenland into its place and was I could do this all day but you should check out this this Mercator puzzle it's pretty fun if you just type Mercator puzzle onto Google you'll find it hi I'm sorry oh sorry you late no problem CJ Cregg where's you are i'm dr. john fallow dr. cynthia sales and professor donald yuke yuke yuke okay and you are the organization of cartographers for social equality well we're we're from the Oh si si we have many members Oh many 4,300 dues-paying members what are the dues that $20 a year for the newsletter let's start this is Josh Lyman did you or Josh this is dr. fallow and Mike News Merry Men yes quaint a simple we'd like president Bartlet to aggressively support legislation that would make it mandatory for every public school in America to teach geography using the Peters projection map instead of the traditional Mercator give me 200 bucks and it's done really no why are we changing maps because CJ the Mercator projection has fostered European imperialist attitudes for centuries and created an ethnic bias against the third world really the german cartographer Mercator originally designed this map in 1569 as a navigational tool for European sailors the map enlarges areas at the poles to create straight lines of constant bearing or geographic direction so it makes it easier to cross an ocean but yes it distorts the relative size of nations and continents are you saying the map is wrong oh dear yes now look at Greenland okay now look at Africa okay you two land masses appear to be roughly the same size yes what a blow your mind I told you that Africa is in reality 14 times larger yes here we have Europe drawn considerably larger than South America when it's six point nine million square miles South America has almost double the size of Europe's 3.8 million Alaska appears three times as large as Mexico when Mexico is larger by 0.1 million square miles Germany appears in the middle of the map once in the northernmost quarter of the earth-boy relative size is one thing but you're telling me that Germany isn't where we think it is nothing is where you think it is where is it I'm glad you asked the Peters projection it has fidelity of axis fidelity of position east-west lines are parallel and intersect north-south axes at right angles what tell is that it's where you've been living this whole time should we continue so you're probably wondering what all of this has to do with social equality no I'm wondering where France really is guys we want to thank you very much for coming in hang on we're gonna finish this okay what do maps have to do with social equality you asked she asked Salvatore Anatoly of the National Council for social studies argues in our society we unconsciously equate size with importance and even power I'm gonna check in on time go these guys find Brigadoon on that map you'll call me right probably not okay when third world countries are misrepresented they're likely to be valued less when where cater maps exaggerate the importance of Western civilization when the top of the map is given him northern hemisphere the bottom is given of a southern then people will tend to adopt top and bottom attitudes but wait huh where else could you put the northern hemisphere but on the top on the bottom how like this yeah but you can't do that why not cuz it's freaking me out so that video was kind of you know a little ridiculous but it is pulling bringing up a nice point that you know a lot of the times when we see our maps we don't really you know think about them in the 3d form and so then we can get these distortions on what we see on the world and so we should really start thinking about that especially whenever we're gonna be designing maps and this is one of my friends who actually did a big tattoo on her back of a map a lot of people do tattoos and maps on their bodies and but they often don't think about the projection but she did think about the projection when she did hers and this is from Karl Zimmer's book called science Inc you should check it out very nice book but whenever she chose the which projections he used for her map for her for her back tattoo she used this tree be equal area projection which is a poly conic so as multiple colleagues put together and she'd spend a lot of time thinking about this and because she knew that it was communicating something and so in this case this maps for her it communicates in Afrocentric world instead of a Eurocentric world it does a better job preserving areas and so that's why she ended up choosing it so whenever you're just making your maps in GIS you got to spend a little bit of time thinking about what projections should use and again it all comes down to what you're planning on communicating to your map reader and so there's two projections monent many of our mouths gonna be looking at when we start zooming in on a regional level and so we're gonna start thinking about um just should we use a transverse Mercator or lambert conformal conic the transverse Mercator again target is going to be best for the north-south orientation of the of your study areas so you can think about California and the lab recur for mechanics though are gonna be better for the east-west remember so should be thinking about a Tennessee and so the reason why we're doing this and it's because the way the air gets distributed across the projection so you can see here is the transverse Mercator projection and it's gonna have to sequence here you can see here this line in that line that's going to be the areas where the transverse Mercator actually intersects the the surface of the earth and so from here for example anything in between these two lines you're going to be projecting downwards towards the from the from the planet to the plane and then on the ones that were here are going to be projecting outwards so this going to distribute out that factor and screw tribute out that error and so you see here for example the scale factor is gonna start becoming exaggerated here in the outside of the lines you see so scale factor greater than one but inside it's going to be less than so you're getting a little bit of shrinkage happening so whenever you're choosing a projection you gotta choose where to intersect those lines so if this was your fictitious place that you're trying to map out the places that you'd want to intersect your lines about 1/6 or so to the to the edge of the border so you can see here about 1/6 when it's a 1/5 1/5 and you can choose your your-your-your reading here which is going to be your longitude and then you also have to choose here an origin of latitude and longitude which that's going to become your central meridian in your origin latitude and then you usually choose a scale factor but typically scale factor is about one if not it's about 0.999 six that's almost one that gets kind of in the wash or whatever for Larrick or formal conics so you can see here when you can perfect compare the lambert conformal conformal conic to the transverse Mercator you see how the transverse transverse Mercator has these lines here these secant lines which we're calling them here the secant lines are actually oriented up down you see how this is even more I'm sorry is having less distortion here because of the way of its orientation but look at the Lambert conformal conic which has its it's parallel just here stamp real wants to learn parallel to which Orient's this way so it's actually easier for you to be able to distribute the error with this kind of east-west orientation and to get the better idea of this we can see this in the next slide coming up but of how the error is distributed and but before we do that you should pay attention to also this easting and northing so you can see here whenever you're choosing is a projection you put in a false easting and northing and the reason why you're doing that the reason why you're doing that is because you're trying to get into positive space which or coordinates so you can see that with the X Y in the top right hand coordinate is all positive but if we don't move the the center the of the axes off to the edge of the the study area must end up happening is that we end up having this mix of negative and positive coordinates which can become very confusing whenever you're working and so you want to move that origin of latitude and and central and Meridian off to the side and that's what's happening here with the western extent and eastern and southern extent whenever you measure those western and southern extents you take that measurement and you make that into your false easting your and your false northing and then what ends up happening is it moves the central Meridian origin latitude out to encompass the whole study area into impure positives so let's move on and this say we want to make our own custom projections so this is what we're gonna do so we're gonna first say what statham are we working in so here we're in brazil peru trans-border region we're gonna say okay mmm we're gonna maybe working in a projection of w GS 83 for example so wgs84 sorry and you can see here why were you making a projection here one of the reasons why we can make we can end up in situation where we need to make a projection is because this kind of type of administrative boundary trans-border regions where there isn't an administrative state that's making a projection that's gonna fit perfect for the areas because normally when people ask me what projections should I use I tell them go see what the official projection is of that breed of that administration that controls that area so if it's a city go check out the city and see what their official projection that they're using our or try to copy the map that they're using because then that way you're you're kind of with their standards someone over there thought about it and decided oh this is a good projection to use if you look here though in this case of Peru and Brazil you're not going to have that happening because if you use a Peruvian projections are going to be made for Peru and the Brazil projects were made for Brazilians and so in this area to get a perfect projection for this area that's independent of administrative boundaries we had to actually make our own projection if we look here we can see that this is bigger east to west so will you say hmm we need to use a Lambert conformal conic projection because that's more like a Tennessee so that's why we should use but let's say and here it is if we actually put Lambert conformal conic so if I'd say okay about one fifth into the top I'm gonna put the line see a line those are the green lines there this word you actually had to touch and remember that's not worry that's where you're getting no error at all but then what you can see here that's going on is that you're having the error being distributed pretty nicely I'm not going to much so he's here from one it goes down to 0.996 and then over at the top again so two point zero zero zero six you get this just this distribution of error very even so you're pretty close to it at all times if we said oh we're gonna use transverse mercator instead we're gonna get this kind of situation where the transition Mercator lines are going to have to be this is the best place so I can find to get him to where we can have point 996 in the middle area but then looking at what goes on on the outside we end up with point zero zero one six remember we have point zero zeros six as the highest or a number of exaggeration happening so you're having more exaggeration happening at the outside parts of it because of the fact that it's a little bit stretched out east to west so in this case you should use a Lambert conformal conic and then you take those readings forward making that that customized projection some length units that are also built into projections you have to decide what length units you're working in and so you have it so you have length units here so for example you have the meters you can choose meter or you can choose international foot or survey for leaders between international foot and survey foot is the kind of number of decimal places that there's in there there's a you see here the the u.s. survey foots at 1200 divided by 397 meters which gets it very like like a high number of precision on the amount of decimal places international foot stays at point zero three four meters it doesn't matter if we're really which one you use in most cases also you have and then you also think about arial 'arial units you have a acres but then you also have the hectare that's in the scientific notation and you also commonly work in square miles so you got to think about those things when we report numbers and your projections and lastly I think about angular units so many times in the projections we're gonna have things like longitude latitude that are going to be defined by the center the earth angles out in degrees so there's 360 degrees in a circle and so you got to think about it that in there's 26 degrees the circle we divided to eat it's a western and eastern hemisphere and so you're not going to ever have more than 180 and then at the time also you got it also in an in a degree you you have 60 minutes and one in every minute you have 60 seconds where or in a degree at 3600 seconds and so anytime that you're working with longitude latitude in computers we like to work in decimal degrees but whenever we talk about launches latitude we usually report degrees minutes seconds and so anytime you want to work in between you're not to do a conversion so just keep that in mind you have to convert into degrees by dividing minutes by 16 dividing through seconds by 3600 but whenever you want to start doing math you have to actually go into radians the only way you can do a lot of geometric math so if you want to start doing measurements across on the curvature of the earth you'll have to actually use radians which is gonna be in units of pi so let's talk about some of the projection systems that are out there in the world we have a global grid with a universal transverse Mercator projection you can find UTM projections UTM zones and you're gonna have predefined projections so for example if you look in Texas region you'll find that it's in zone 14 in Central Texas that will already have different settings that you can already bring in and it says kind of a stand that's set already and so a lot of times UTM is a great projection to use for regional mapping because it already has already been kind of calibrated to do really good mapping but if you go and zoom in Oh so also if you look here at other kinds of projections out there like for example Maidenhead a lot of times these kind of projections they break up everything into character readings and so as opposed to zone numbers like in UTM these are going to be read off us character numbers and so you can see here like we have column E for Austin Texas and then we have the row M and so if we wanted to find the map projection for that in Medan we would say okay we want a.m. and that would give us a nice projection but they also have further going in where you can break up eeehm into into other pieces and so here you see I call them one in row zero and so we can start putting these things together and saying am ten and then we can have a projection for am ten that's already been made for us that's also going to be useful and then we can go even further in and we go into M ten and then you have a sub square there of D and G and so you start reading it off as a M 10 DG and that would be the projection that would be the the map that you would the projection map that you would use for that you had the same kind of thing happening in the world geographic reference system GeoRef where you can take the column and then the row and column letters so F J and then you break that up and you look into it and that's broken up into additional letters of H a and so you start putting things together like FJ h a 4460 and so forth to get the G or F and that's actually and it gives you a pretty accurate launch through latitude reading at some point so you can actually start reading off letter and number systems like this in order to to get work as a longitude latitude also in in mapping this is a good time to talk about the United States public land survey so besides the original 13 and in Texas the rest of United States was kind divot up and to into town shipping ranges and they just call it township and range there's just rows and columns and so each one of these the states were divvied up into these lines to make to make some like the original deeds and so forth and so you can see here they end up becoming a bunch of little squares and so you can see if you go to one particular square and you check it out you'll find out that it's Township number three south and range 33 es these township and range become really important in land disputes for in the united states because a lot of legal battles about these because again these were made a long time ago and now we have high-tech maps and so sometimes you find out that people's land deeds are you know one meter off or something because of the township and range definitions back in the past and so that's something just to keep in keep in mind with the township and range from the unit from the united states land survey and so also you have here state grids that exist as well like in texas they have their own state grid and then we also have all the in the united states we have a state plain system and projections state plane systems are buying far more popular than the UTM projection when you start getting its a local level UTM is really good for things like it's a the county level but once you start getting into the city level a lot of times people want to work with state planes and these are going to be a little bit better than museums in some cases and so the state plain mapping system is really mixture projections there's transverse mercator x' network or formal conics oblique marketers and new teams and it's gonna be the best projection to use on a local level and so what you to do is find out what which state plane system number you're in and so for example in texas is broken up into five zones and so you have a code 42 that's for the state and in each zone 0 through 5 and so for example with that austin texas example that we're using we bring in travis county and you can see there's 42 over 3 but if you just go south to travis county to Hays County you'll be in 4204 and anyways these projections are going to be the best projections to use for kind of almost survey grade mapping and you can see here how the texas central lambert conformal conic smade there's gonna be the parallel to parallel one there you can see how it's distributing the error in between if you start getting too far outside of that you're going to end up getting there you end up getting too much distortion so we have to be careful like say if you were mapping out things in San Antonio you're really gonna want to go and use the the 4204 projection because if you're trying it with O three you're gonna get too far out are gonna be exaggerating out your values but in other cases like hearin for example vermont the the whole state basically fits in in a UTM zone and so it basically uses a transverse Mercator system it only has one projection so 4400 that's prover that's four Vermont 44 for the state code for mod 0 0 because there's only one and you can see here the whole state fits into it quite nicely and with those settings there you're going to get the best kind of regional mapping that you can get out there but in some cases like in Alaska where you have this weird kind of situation happening where the state has this these islands kind of are capitolio kind of area of the coastline but that's next to Canada that area there is going to be better to map with oblique Mercator projection because then it only has one zone for that whole area as opposed to having multiple zones because you're stuck with the north-south kind of thing so you here you use an oblique Mercator such a transverse Mercator another thing to keep in mind is that the 7.5 minute quadrangles is one of the more popular naming systems where you get the topographic maps from the United States Geological Survey the USGS topo maps for seven point five minutes that's their highest resolution map that they provide and if you see from their Maps they're gonna have the maps the whole United States sectioned off into little squares and those squares are going to be given there are seven point five minutes of longitude by seven point five minutes latitude so their squares in in launched latitude but in reality the way they look after you provide projections on them and so forth they end up looking like rectangles but you can see here that the actual latitude/longitude grids are a little bit different to paint on if you use that 27 wgs84 if you used UTM 1983 those are all like that's one of the issues that can come up in it so whenever you look at these grids and gradalls and you start zooming in on them you'll see here readings on it and it'll tell you things like what the projection was and so here for example the projection on it is going to be the East Zone transverse mercator 1,000 meter transverse Mercator grids for zone 11 so that's using UTM zone 11 with in 1927 North American datum so that's going to be the projection that I use but then you can see here on the side you have launched two lights you've been reported but you're also having the meters being reported from the from the UTM projection zones I said something to keep in mind there so how does all this work in ArcGIS so whenever you're in arcmap you're gonna want to set your coordinate system and GIS and what's what's kind of nice about this is that we have projectile fly which is going to take care of all the kind of different projections that you might be working with you might have a few different projections working in your and your different data files and but then you can display with the current coordinate system you have a display projection that only shows the projection you want to work with and so here you have geographic coordinate systems which is Azeri talk for unprojected UTM projected datums so this is like what just longitude latitude and north american datum is one wgs84 s one so this is one to think about and then that you should never make maps and by the way don't ever make a map in geographic coordinate system the other one is projected coordinate systems and that's going to be over here with the ones that you want to make maps and you're going to find UTM state planes all the grids all that kind of stuff is going to be hanging out there so ESRI actually has a lot of those settings pre-established in it you can always import your own projections or make new affections but it's also nice to have this nice library of lots of projections to use so that's how that's the place where you go you as a data frame properties click on coordinate systems and then you can start switching projections when you do that it's it actually switched to projection on the screen and so this gets into the idea of what is going on with projecting the fly so way back in the day when I was learning GIS has a little weed Ladd I would have to go through and project every single one of my data sets into a common working projection for to be able to actually make to make a map but ESRI has this nice thing called projects on the fly where it has a professional fly engine basically reprojection everything as you zoom around or zoom in or zoom out and redrawing it into the so the corrected projection that you chose so I can bring in for example here three different data layers the topographic or for example income water all with different projections wgs84 State playing 93 but then I can go select the projection here on a different properties and whatever projection I select here is gonna show up as a display projection on the screen because everything is going to go through the projectile flying machine before it shows up on your screen so it's actually really nice because you can bring in this all these different data sets with all these different formats with all these different projections and start working with them in GIS is one of the strongest things I think that comes out of the ER yes all right package so we learned about projections and datums and longitude latitude and everything you could want to know about it and so good luck with your studies and you know hit me up on

Channel: Moulay Anwar Sounny-Slitine

Views: 8,650

Keywords: GIS

Id: dHT0ckOfScU

Length: 56min 56sec (3416 seconds)

Published: Mon May 28 2018