Congressional Districts

 

 

How do Automated scripts compare to hand-drawn methods?

Hand-drawn cartogram of Congressional Districs on the left, ArcView script applied to cartogram on the right.

How they were created

By hand:

The map of Congressional Districts was edited beginning with Adobe Illustrator. To make sure each area is the right size, a standard sized reference box was created and moved over each area. Each district was compared to the box by eye, as they were drawn. The illustrator file was exported as a CAD file, then using ArcToolbox, the CAD file was converted to a GeoDatabase and then to a shapefile so it could be opened in ArcMap. ArcMap was then used to calculate the areas, and choropleth the districts by area. (districts that were too small were colored in a blue monochromatic scale, and the districts that were too large in a red monochromatic scale.)

The edited map was printed and the process started over again with illustrator, moving vertices around some more. (Anytime there was a blue district next to a red district one of the common-vertices could simply be moved into the blue district.) The process was performed three times for good measure.

Automation:


Cartograms produced using an Arcview script, left to right, base map, after 5 iterations, after 10 iterations.

Currently, there are no commercially available software packages to create a cartogram. The best alternative thus far is an ArcView avenue script, but it is not widely used. Each iteration of the script in this example took over 45 minutes. With five, ten or fifteen iterations, it could be quicker and much more aesthetically pleasing to produce a cartogram by hand.

Quoting Steve Demers:

" I definitely prefer for aesthetic purposes, [making a cartogram] by hand. The time you save automating, you end up using anyway fixing everything that the computer screwed up. You can see in several places in the final cartogram where the congressional districts lose topology. ...there is actually a hole in the cartogram. There are just too many things that can go wrong in automation. Making a cartogram takes a lot of cartographic licence, style and creativity- things a computer just cant do."

click for entire photoDisplayed above are the results of running the "contiguous cartogram" Arcscript by Andy Agena, from ESRI.com after 5, 10 and 15 iterations. For an animation, click the image to the right:

Compared to the hand-made image, the computer generated cartogram is not as easily readable.

ArcView Shapefiles are available here (ZIP files):

Base
After 2 iterations
After 7 iterations
After 10 iterations

 

 
 
 
 
 
This site is funded by the USGS, created by Ian Bortins and Steve Demers under the direction of Dr. Keith Clarke, hosted and maintained by NCGIA.

Last Edited 7/29/02