Basic Spatial Analysis Geographic Information Systems (GIS): A Technical Video Lecture

hello and welcome to this GIS tech video on basic spatial analysis with geographic information systems the learning objectives for this lecture are to describe what spatial analysis is describe select basic vectorbase geoprocessing operations for spatial analysis describe select basic raster based spatial analysis operations and compare and contrast various basic spatial analysis methods in industry standard GIS tools through hands-on demonstration a dictionary definition of spatial analysis is that it is the process of examining the locations attributes and relationships of features in spatial data through overlay and other analytical techniques in order to address a question or gain useful knowledge spatial analysis extracts or creates new information from spatial data spatial analysis is a core process supported by GIS software that makes GIS software unique from other analytical tools given the emphasis of examining spatial data and relationships additionally spatial analysis is the driving force behind many GIS software functions in the next part of this lecture I will discuss select examples of different spatial analysis tools spatial analysis tools are often specific to the underlying data model of the data being analyzed with vector based points lines and polygons there are several what are known as geo processing operations many of the vector geoprocessing operations function as input/output operations this means that an input feature like a point line or polygon is used to create a new output feature that is created based on the geoprocessing operation in the next part of this lecture I'll give you some examples of commonly used vector geo processing operations buffer buffer is when an input feature is used to create new output features at certain distance around the input feature for example if we have a point as an input feature we can then tell the buffer geoprocessing operation to give us an area that is 500 meters around the input feature the buffer geoprocessing operator will then create around the input feature a new output feature that is 500 meters around the input feature clip-clip is when a feature called the clip feature is used to extract an area from an input feature to create an output feature one way to think of clip is like making cookies you can think of the clip feature as the cookie cutter and the input feature as the dough from which the cookie is created for example if you have an input feature you can then define a clip feature for the area you want to clip out from the input feature the output feature is then clipped out from the input based on the clip feature used dissolve dissolve is when features are aggregated based on a common attribute for example this image shows census tracts by county as indicated by the different colors dissolve can be used to aggregate the census tracts by county when the dissolve operation using counties as the dissolved attribute is run the output features show how census tracts have been combined or dissolved based on their common attributes Union Union is a function that computes the geometric union of polygon features for example in this image you see three features two blue rectangles and a yellow circle when the Union geoprocessing operation is run a total of five new output features will be created based on where geometric unions between the three original input features were found identity identity is where the geometric intersection of the input features and identity features are computed and portions of import features that overlap identity features will receive attributes of the identity feature for example let's say you have two input features they have an attribute of a for feature 1 and an attribute of B for feature to the identity feature has an attribute of see after the identity geoprocessing operation is run for output features will be created features created where the identity features touch the input features will have attributes of both the input feature and identity feature intersect intersect is where the geometric intersection of input and intersection features is computed for example given a set of input features and an intersect feature after the intersection geoprocessing operation is run the output feature will only have the area where the inputs were intersecting with each other in the next part of this lesson I will discuss select examples of raster based spatial analysis methods raster spatial analysis works on doing calculations of raster grid cell values one way to begin understanding raster based spatial analysis is map algebra map algebra is the idea of doing various mathematical operations on raster cells to create a new output raster for example let's say you have two raster data files in this example colors in each saw represent the same cell in each rafter in terms of spatial extent for example the blue cell at the top of rafter one is the same cell in terms of spatial extent as the blue cell in the top of raster 2 using simple map algebra the two rafters can be added together on a cell by cell basis this in turn creates a new output raster that has the combined values of the two input rafters another example of map algebra is multiplying raster cells by a constant value for example many digital elevation models or DMS contain topographic cell values that are in metric like scene in this hypothetical example given that there are three point two eight feet to a meter each cell value can be multiplied by a constant value of three point two eight to create a new output raster that contains the cell values based on the multiplication of the input raster by the constant and in this example creating a new raster grid with feet based cell values instead of metric values in the following slides I'll give you few more examples of common raster analysis methods slope slope is the idea of calculating the maximum change rate between a cell and its neighbors for example here we see a digital elevation model of a mountainous area after the slope tool runs in output is created indicating the degree of change between cells slope is commonly used with elevation datasets and in site selection problems where it is necessary to determine flat areas hillshade hill shade is where the sun's relative position is taken into account to create an output greyscale representation surface you can think of the hill shade like shining a light over a topographic surface the altitude and azimuth or compass angle of the light source will determine how the shadowing in the hill shade surface is created for example using the previous elevation surface we can run the hill shade command to create the output hill shade in this example the default azimuth of 315 degrees along with an altitude of 45 degrees from the horizon was used as the light source thus creating the darker areas under some of the mountainous Peaks as seen here due to shadowing Euclidean distance Euclidean distance describes each raster cells relationship to a source or set of sources based on the straight line or Euclidean distance for example let's say you need to know the distance between hospitals for planning a disaster evacuation this figure shows examples of source cells which in this example are locations of hospitals after Euclidean distances run in output raster is created that shows distances between the source cells or in this case hospitals such information could be helpful for planning distance between evacuation activities as to which hospitals injured people should be sent to in the next part of this lesson I'll give you a hands-on demonstration of some of the techniques previously discussed in this hands-on demonstration I'll give you an example of using some of the vector based geoprocessing tools you learned about for a hypothetical spatial analysis specifically I will do an archaeological sensitivity spatial analysis the analysis will be to see what areas inside a 500-foot buffer of a proposed interstate reroute are archaeologically sensitive for example are there any Native American or historical structures that should be accounted for before construction of the interstate begins to facilitate our spatial analysis we will use a simple model to develop a final area archaeological sensitivity score specifically we will calculate distances from historical structures times distance from water to derive an archaeological sensitivity score the following image also helps illustrate this ideas in terms of the final output from the spatial analysis this image shows an example of the study area the red line indicates where the proposed interstate reroute is being planned this is in relation to the existing interstate that is to the east or right of the reroute this dotted line represents the 500 foot buffer around the proposed interstate reroute that is of interest for the archaeological sensitivity analysis finally these polygons represent areas determined to be of archaeological sensitivity based on the spatial analysis and modeling conducted using the parameters discussed in the previous slide in this hands-on demo I'll show you how to do such a spatial analysis and model I'll also show you how to create a basic elevation effect using some of the raster techniques previously discussed this happens on demonstration we'll do an archaeological site sensitivity model using some basic vector geo processing operations now one important thing to keep in mind when you're doing geoprocessing is the input/output factor of those operations so well the first thing you want to do when creating a new map document is actually created default geodatabase so let's go over that first so I have an unsaved map document here and I'm going to save it near my datasets I have set up for this so by doing that you can see over here in our catalog my map document is next to some of my data set so I'll use for this demo but an important thing I want to do here is go file map document properties you can see here it says default geodatabase because of all the input and output we're going to be doing we want to know exactly where our outputs are going and the system default geodatabase is okay but if you're planning to move your data around off of different computers it's really helpful to have your own default geodatabase so I'm gonna click here and I'm going to go in my home directory and click right here where it says new file geodatabase and I'm gonna rename it and call it output and it's a little tricky with the clicks here but rename it click off and click back on it again you can see it changes it here and I'm also going to store relative pathnames that'll make sure that all of my de ST is relative to my mxd in case I need to move it so we've got that set up now the very first thing I want to do is bring in some of these data sets so back to our original discussion about what this model and analysis will be we're going to look at archaeological sensitivity to a proposed interstate reroute so I'll bring that first bring over there reroute data and it's gonna be a simple line feature and I'll just ignore that and we'll make that maybe a little more clear color make it stick out good so this is the area that we're going to be interested in 500 feet around in terms of archaeological sensitivity now I also have some historic data to give some context for example I can bring in here we see a historic map of my study area from the 19th century and I had previously digitized some of the buildings off of this map so I'll bring those in and I'll make those stick out a little better to maybe I'll make them red a little bigger so we can see what's going on so we zoom in a little closer we can see how there could be some areas here's the proposed reroute the red line and structures near that reroute that have been digitized off a historic map now we're also going to bring in water as per the original model we're interested in distance between distance from I should say buildings and from water so I'll bring a water layer in and I'll make that a little clearer to see as well make that blue for water and so forth so here's the spatial relationships we're interested in we have the proposed reroute in red water and structure shown as dots now to set things up as well I'm going to actually add a new field to the structures to give those structures a point value for calculation with other outputs and that'll become more apparent as I move through this but what I'm going to do is I'm going to go to the attribute table of structures and I'm going to click add field and I'm gonna call it struck down for structure value I'll keep it a short integer and I'll hit OK and you can see the little around all and then I'm going to use the field calculator and I'm just gonna give them a number ten and that's a very arbitrary choice you could make that any number you want when you see the final output of this it'll probably make more sense why I'm doing it with ten but it really could be any number and that's a much bigger topic in terms of spatial modeling and weights and so forth I'm just gonna go ahead and use field calculator so now every structure has this arbitrary sort of weight of ten given to it okay so now let me show you how buffer works the first thing we want to do is create a 500 foot buffer around the interstate rear I'll turn a few layers off to make this more apparent loom to that layer and for your own training there's several ways you can actually go about running the geoprocessing tools in newer versions of arcmap they now have this handy menu right here with some of the more common ones that you saw in the earlier parts of the video but just for thoroughness of the training you also have a search tool where you can type the name of the tool in that you want and this gives me one buffer analysis you also have our toolbox that if you get really good with our map you can hunt around through here and go analysis tools proximity buffer so I find that there's so many tools I often just use the search tool but you can get to it as well through our toolbox or through the geoprocessing menu up here but in this case we're just going to use the tool that we're going to access it here and in this case real straightforward here if you use a lot of these tools input and output like you learned about earlier we're gonna pick propose 390 reroute and notice here now the output feature class by default is going to that output geodatabase we created in the beginning so I'll just leave that default you can see it's going to give me a name the name of what I'm buffering plus underscore buffer and in this case we want 500 feet so I'll change that here and we'll just leave all the defaults and so forth so with that I'll set up I'll move this over so you can see I'll close a few things too we'll hit okay we'll watch it run like any kind of tool make sure you look down on the bottom right to see the tool running and there comes our very first buffer as part of this modeling test we zoom in a little closer you can see the output and so forth and it's our to automatically add it to our map now we're gonna save it okay now you can actually do buffers multiple ring buffers at multiple distances in this case we're going to have our water sensitivity be factored by multiple distances from water so again I'll turn that layer back on and we zoom out a little bit to slick at those spatial relationships so forth so now let's do buffer again this time a multi ring buffer for the water layer so in this case we actually have to use a slightly different tool to create a multi ring buffer and I'm going to get to that by going back to the search tool and I'm going to type in multi ring buffer as you can see there's a slightly different tool but again that search box can be very handy for finding what exactly does you need so I open this up and you can see now has a similar kind of interface but slightly different parameters you put in so in this case I'm going to do Livingston hydro sub set again here we see that default geodatabase live hydro sub set multi ring and the first distance I want is going to be 250 feet and the next distance is going to be 500 feet I use the plus sign to add that so input is the live hydro sub set water output is going to be sent to my default geodatabase and I'm going to get two buffers created based on this based on these distances I've inputted in the list you can see you could have a lot more I'll leave all the other defaults as neaby and I'll run this tool and like always I look down here just to make sure my output is happening okay and we can see here that the multi ring buffer ran correctly so I'll make the screen a little more visible here now this is a good example too of how things can quickly start getting visually cluttered and a lot going on here but it looks kind of interesting so to kind of summarize where we're at we just ran a multi ring buffer of the water sources at five hundred and 250 feet and we're now going to start looking at the relationship of those with your reroute buffer of a road and the next thing we need to do now is do a buffer of distance from structures and in this case we're going to do a 1,000 foot buffer around the structures now again that's a very arbitrary number that I picked and that's sort of the challenge of doing modeling is how you determine distances and how you determine weights and so forth but since this is more focused on just showing what the tools can do we're not going to worry about that too much and we'll go ahead and do a buffer of the structures so again I'll use it by getting up here now in the previous examples of buffers I haven't really changed at any of the other parameters but in this case I am going to change and I'll show you what I'm going to do so in this case I'm going to select structures as the input again my default geodatabase is set up to receive my output I'm gonna set it to 1,000 feet and if you look at some of these other parameters down here one of them is dissolve dissolve type and so far we've we've been selecting we've been dissolving things but in this case we're going to leave it as none and that means that every one of those little red dots is going to have its own individual buffer circle around it and that's different than what we saw with the stream buffer where there was basically one feature created one buffer feature created per feature so in this case I'll hit OK watch this run as always we're looking down here you can see in this case now zoom in a little closer on what we have like I said every one of those red circles I'm sorry right every one of those red dots created its own individual buffer circle and if we look at the attribute table you can see that we have a lot of buffers 182 got created and so forth and you can see two in the output that struck Val came the structure of value came along and we're going to see what that does for us in just a moment okay so the next thing we're going to do now is we're interested in you the structures buffer with the multi ring buffer of the water so we take a closer look just at those two and so forth there's the proposed reroute in red here we can see lots of overt spacial overlaps between distance from the streams shown in blue and distance from structures and we're interested now in it in terms of spatial analysis and seeing sort of combinations of these areas based on scoring and what I'm going to do for that now is use the Union so what I'm interested in doing is combining the multi ring buffer of water with the buffer of the structures and by doing that Union it'll also combine their attributes together so again it's very handy for this particular one I'm going to go to geoprocessing Union and you can see here like you saw with the multi ring buffer I have a list of features I can add to the Union tool so in this case I'm going to do the multi ring buffer of hydro or water and then also the structures buffer I'm going to put those together and I've got a little warning that's not a big problem yellow means you can still go I'm not gonna worry about it again here's my default geodatabase all set to receive that we're gonna join all the attributes and we're gonna let this run okay now we have that warning about the data but we're not too worried about that now we can see things are getting really sort of visually interesting here so now this is our union of the two buffers and you can see it's very messy sort of looking but it's actually a good thing because attributes from the two buffers are now part of this output buffer and we look at the attribute table here when you see a struck Val of zero that means a spot where the water buffer did not touch a structure whereas when you see a struck fail of ten that means there was a structure there but if it's over here means with zero means there wasn't a water and so forth so what we're gonna do now is we're going to basically do multiplication between this field and this field to look for cases where there was an overlap so for example a distance of 250 times 10 or a distance of 500 times 10 and so forth and that should give us three output categories because anything multiplying by zero will come out as zero so to do that I'm going to create a new field called score I'll make it a short integer and I'm gonna right-click on that new field and use our field calculator again and this case score is going to be equal to the distance which was the attribute that came in from the multi rang string buffer as part of the Union times the structure value and that's it so a simple multiplication of those two fields to give me a score value and I'll hit OK and you can see here now I've got values of 0 2,500 or 5,000 3 categories okay from that I can do a quick symbolization if I go to the properties and you can start to see now anything in green was zero anything in sort of this purple color was 2500 and anything in 5000 is the pink color and so I'm going to save my work and now as you can see this is very cluttered and messy and this seems like a really good job now for the dissolve tool because at this point I have either no sensitivity medium sensitivity or high sensitivity so again I'll use from this handy menu here geoprocessing dissolve and my input is going to be this one right here that for my Union and I'm gonna call this one I'll call it the final because we're getting close to the end here and and with the dissolve I'm now going to dissolve as you remember dissolve is based on in common attributes in this case score there's only three unique score value 0 2500 or 5000 I'll leave all the defaults I'll hit OK and you can see here a dissolve cleans it up a little bit by comparison to what was underneath it and I can turn that one off now if I go look at the attribute table here you can see we've got just basically it dissolved everything down into 3 either 0 2500 or 5000 and again I can symbolize this to make it a little more intuitive based on categories unique values I'll add those all in there maybe use a different color ramp this time to make it a little easier to read uncheck that and here you can see our output so again zeros now we could even in terms of symbology if you're not interested in those not sensitive areas and so forth okay now finally to pare this down we go back to the original goal this analysis we're interested in sensitive areas that are within 500 foot buffer of of the proposed interstate reroute I'll change the symbology symbology of that buffer I'll make it red little thicker as you saw in the graphic I can also maybe make it a different kind of line type like one of the say dashed lines it's really up to you whatever you think is best but I'll do something like that so we're basically interested in just these areas from the dashed line in inside the buffer and this is a good example now where we can use the clip tool so basically the clip feature is going to be the buffer the proposed 390 reroute buffer and we're going to clip out areas from that final that are sensitive so to use this tool again we go to geoprocessing clip the input features are going to be the final layer the clip feature is going to be the proposed 390 reroute buffer once again we have it all going in at our default geodatabase we'll ignore the optional parameters we'll hit OK and here we now have the final clip and there's our final product from this analysis so we you can see now that it clipped it out just inside that buffer again we can do the symbology on it we can change the labels around perhaps we can remove this one out to get a sense of things and if we look at that now in relation to say some of the historic data that we used originally you can see kind of where things came from like some of these structures down here and so forth now last thing I want to show you real quick is how you can go about maybe creating a background for this with some raster data I do have a digital elevation model of this study area and we'll bring that in and you can see that this digital elevation model is relevant to maybe this part of the of the study area you might do this to create some context and so forth if you're not happy with some of the other default options and arcmap gives you and so forth so to do that we're gonna first what we'll first do with our DM is will change its symbolization and we'll use an elevation ramp like you saw some of the graphics I used earlier in the video something like that okay and we'll turn that final clip off just for demonstration now again if you don't know where to find the tools you can use search to use we're going to use the hillshade tool and you do need the spatial analyst extension so to make sure you have the spatial analyst extension you go to customize extensions spatial analyst if the extensions not turned out make sure you check that box there and close and then again well I'll use the the search tool to find it it's called hillshade and we want hillshade spatial analyst and again it's very easy to use tool it's an input output the input raster in this case will be the DM the output here again once again we see our default geodatabase I'll leave the azimuth and altitude values by their defaults I'll hit OK and you can see we get the hill shade gets created behind us here and now you can do an interesting basic visual effect by taking the DM putting it on top of the hill shade going back to the DM go to its properties and change its display its transparency to say 50% and that will make the colors transparent to kind of reveal the hill shade behind it with a color color color and pattern and you can see we kind of get a neat effect with that with looking at like a stream and so forth so that if you were then go build your final map product from your analysis and so forth you can add a little more context of things so also should note again that default geodatabase here's all those outputs were created in one nice spot that's why it's important to keep everything all together so I hope you enjoyed this demonstration and again like I said earlier in the video keep these ideas in mind around spatial modeling in terms of weights parameters and so forth there's much much more that can be done with these techniques in this lecture you learned how to describe what spatial analysis is and that spatial analysis is a core process supported by GIS software that makes GIS software unique from other analytical tools given the emphasis of examining spatial data and relationships you also learned how to describe basic vector geo processing operations for spatial analysis such as buffer clip dissolve union identity and intersect keep in mind too that these were just a selection of the most common vector based geo processing operations you should further explore geo processing capabilities of your GAF software to see what other geoprocessing spatial analysis options exist for you you'll also learn how to describe basic raster based spatial analysis operation such as basic math algebra slope hill shade and Euclidean distance like the vector tools I only showed you a small example of the many raster based spatial analysis tool that exists and you should conduct your own further research to find raster based spatial analysis tools that match your spatial analysis needs finally I showed you how to compare and contrast various basic spatial analysis methods in an industry standard GIS tool through hands-on demonstration using an example of archaeological site sensitivity modeling spatial analysis and modeling is perhaps one most powerful aspects of GIS in terms of decision making and spatial insight I strongly encourage you to use the idea from this lecture at the starting point for your own spatial analysis the following are references used in preparing this lecture if you enjoyed this GIS tech video or have any comments or questions feel free to contact me at the email address below thank you for watching

Channel: GIScience

Views: 25,000

Rating: 4.9072847 out of 5

Keywords: GIS, Spatial Analysis, Geoprocessing, Buffer, Clip, Vector, Raster, Modeling, Spatial

Id: HnlqXXhu9HA

Length: 37min 43sec (2263 seconds)

Published: Tue Mar 07 2017