39. Graduated Symbol Mapping with ArcMap

in this video I'll show you how to make graduated symbol maps with arcmap you do this pretty much the same way that you make proportional symbol Maps or choropleth maps in the symbology tab of the layer properties so I'm going to come up to this counties layer that I have and right-click and go to properties and then in symbology under quantities I have the option for graduated symbols so I'll click on that and let's look at making graduated symbols to symbolize the number of people within each of these counties that are aged 65 and up so this is going to be mapping the elderly population within the US if I select that you can see that I get classes the same way that I do for graduated colors or what's called a choropleth map and each of those classes has range for the data that's stored for each one of those counties and then a size of the symbol that's associated with that it's nice to be able to classify the data and then specify the exact size of the symbol that should be used for each one of those classes because it allows you to have realistically sized symbols even with data that has a very large range so I'm going to go ahead and apply this and you can see how these symbols are going to distribute themselves in the map we've got larger symbols and counties where there's a large elderly population and then relatively small ones and counties that have a small elderly population if I was to use proportional symbols for the same variable even with a relatively small minimum value symbol for these counties that have relatively few elderly people in them I'm going to have enormous circles for the counties that have very many elderly people in them especially their urban counties that just have a lot of people to begin with in them and so it's nice to be able to use these graduated symbols because you can control the maximum size of the symbol and rather than having symbols that are proportional and therefore make your large symbols extremely large you can just have larger symbols as opposed to smaller symbols and so this is an ordinal ranking rather than a proportional ranking but it does work well for these distributions of data that are very large so I'm going to come back to graduated symbols and hit apply and you can see here that we have some similar issues to what we did with our choropleth map and that we're essentially just seeing the areas of the country that have large populations to begin with and therefore have more elderly people now it's okay to use raw counts with graduated symbols because the symbols are actually denoting a certain size of population you have a large symbol you have a large and it's not distributing that population over a large area as you would with a choropleth map if you filled in the entire county so it's not really giving greater weight to larger areas and therefore it's not falsifying your data based on the size of the area unit that you're mapping at the same time it still can be nice to normalize your data so I can come back over here and normalize by for instance the total population in 2000 and again you'll see this paints a pretty different picture the circles are more similar in size because the proportion of the elderly population to the overall population is going to be more similar across the map than just the raw count of elderly people but again you do see an interesting pattern you see that there's quite a sort of you see that there's sort of a break from the Great Plains East where there's a fairly constant density of elderly population across the map you can see that there's some areas down in the southeast shore where there's an especially low elderly population and then here in the Rocky Mountains there's a relatively low elderly population in some of these very rural areas I'm going to go back and remove the normalization just because I think it's a more provoking map it's a little bit easier to read you can see these populations popping out in urban areas but you can also see that there's a high density of these high elderly population urban areas down in Florida and along the Northeast seaboard and a little bit in California so there are some interesting patterns that come out here

Channel: middgeographyCH

Views: 12,449

Rating: 5 out of 5

Keywords: Middlebury, Sptial Visualization

Id: NWeM4NpwaCo

Length: 3min 32sec (212 seconds)

Published: Thu Apr 07 2011