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."
Displayed
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
