How to create thematic (choropleth) maps in ArcGIS, Part I

now in this video we're going to quickly walk through the basics of creating a thematic or a choropleth map which basically means that I have some area that I want to represent by a range of values that represent something so of course the first thing that I need is some data so from within ArcGIS I'm going to click on the add data button and find my data set now for this example what I'm actually using is the New York City Community Health Survey data which is available that's what I find it is just by doing an internet search for Community Health Survey GIS data and what this represents is essentially a whole bunch of health indicators across New York City and they will all be percentiles I can take a quick look at my entropy table just to see what's in this data set I right-click on the layer and click open attribute table I can essentially browse the entire data set now I'm already familiar with this data set so I know that ultimately what I'm after is one of these columns and again these represent some percent of some health indicator now if I didn't know what one of these variables represented an easy way to find out is to simply look at files metadata and metadata can be opened directly in arcgis by right clicking on the layer you're interested in going down to the data option and clicking view metadata now all files should have metadata but not all GIS files do but if I'm fortunate and I do have metadata essentially it's going to give me a lot of basic information about the dataset that I'm working with and by clicking on attributes I can find the listing of the same columns that I was just looking at in the data table and perhaps I find something that I'm interested in making a map out in this example I'll use the diabetes variable dye about 2 so here's my definition so closing the metadata I can go back here now remember you can rename layers with an ArcGIS you're not actually going to be harming that data or physically otherwise changing the file name and to do that I can slowly click on the file name and I know that this is going to represent my percent of people told of ever having diabetes alright so from here what I really want to do is begin symbolizing my data using that variable that I found and the easiest way to begin doing that is simply by double clicking on layer making sure I'm on the symbology tab and clicking on the quantities option now when I click on the quantities option I'll have the opportunity to select the variable that I was interested in because essentially it's pulling the column directly from the file so I find that diabetes variable again here and select it now as soon as I do our GIS is going to take my value and divide it into a number of classes and by default it's going to use a natural breaks or Jenks classification or method and it's going to assign five classes now for the purpose of this data what I'm really interested in is quartiles so to begin what I'm going to do is change this from five to four classes and then click on the classify button now from the classification window I can select a different method for breaking up my data and in this case I want the quantile method when I select it I'll see for my histogram that my breaks are actually changing and I still have my four classes now one thing that I know about this data is it includes some areas that actually don't have any data these areas are essentially central park in the two airports so I want to remove those from consideration for my quantile method to do that I click on the exclusion button from the data exclusion properties window I can find my variable again and since this is something that I'm going to be excluding from consideration when I begin symbolizing my map I need to find the same variable select it and finish building my query so we can see what it's doing here click on the equals button and if I want to I can get all unique values for that particular column and I want to remove 0 so I selected here I can verify my expression by clicking on the verify button and assuming all goes well I can now click OK and my histogram is actually readjusted to represent what should be now the correct quantile classification for this particular variable so once you're satisfied go ahead and click OK now while I'm in this layer properties window I'm also going to fix the way that it's labeling my data now you could simply click on these and change them by typing in new values but another way to do it is by clicking on this label header or this label button which will let you format the labels now again I already know that these represent percentages so I'm going to click on percentage click on numeric options to remove some of the extra decimal places leaving 2 or 1 is a good idea click OK click OK and now this is looking better so again if I want to I can still click on each one of these labels and add additional information or change how the information is being represented it's not actually changing your range so it looks pretty good I'm now going to hit apply and if I move my layer properties window out of the way I can begin getting a picture of what's actually happening now if that looks good great if I want to I can change my color ramp to something else maybe clean up my cymbals a little bit either by individually clicking on them or working on them in a group and once I'm ready click okay and now my maps starting to come together now a reminder I lost some areas I had some areas down here and up here and Central Park represented in my original file now I like to include those areas because technically otherwise the risk is that this begins to look like the coast and it's not so what I can do is go back to my add data button select the layer again add it in remember that it draws in order from the top to bottom so I'm going to drag this top layer by selecting it holding down my left button and simply dragging it below my diabetes ever variable and maybe changing this color to something more neutral and now my map has the areas represented but they're not distracting or otherwise taking away from the message of my map so that's in essence how I begin building a one variable map in future videos what we'll talk about is actually finishing this map adding a legend scale bar North arrow title some other things and also how to add a second variable on top

Channel: Chris Goranson

Views: 79,043

Rating: 4.8980894 out of 5

Keywords: GIS, public health, Hunter, CUNY, tutorial, ArcGIS, Map (Literature Subject), How-to (Conference Subject), University, Software, Student, College

Id: bFOrosOuHcY

Length: 9min 22sec (562 seconds)

Published: Mon Oct 04 2010