"Cartography is 27% art." - Steve Demers
A cartogram is a "is a map in which some...variable...is substituted for land area or distance. The geometry...of the map is distorted in order to convey the information of this alternate variable."
A common use of cartograms is to depict world population, with nations sized according to their population rather than their area:
A cartogram is a type of graphic that depicts attributes of geographic objects as the object's area. Because a cartogram does not depict geographic space, but rather changes the size of objects depending on a certain attribute, a cartogram is not a true map. Cartograms vary on their degree in which geographic space is changed; some appear very similar to a map, however some look nothing like a map at all. -- National Center for Geographic Information and Analysis
This diary focuses on
electoral college cartograms, in which states are sized according to their number of electoral votes.
(cont'd after the jump)
Non-Continuous Cartograms
In a non-contiguous cartogram, the geographic objects do not have to maintain connectivity with their adjacent objects....By freeing the objects from their adjacent objects, they can grow or shrink in size and still maintain their shape. - National Center for Geographic Information and Analysis
Dr. Paul-Henri Gurian's cartogram of this type is the most prevalent example:
Dorling Cartogram
Dorling cartograms make no attempt to preserve the shape of the geographical object depicted. Instead objects are represented by a uniform shape, typically a circle.
For 2012, the Huffington Post offers a Dorling cartogram as an alternate view of their electoral college calculator.
Demers Cartogram
The Demers Cartogram differs from the Dorling cartogram in that it uses squares rather than circles, which minimizes gaps. Also, while the Dorling cartogram algorithm minimizes the distance each object is moved, the Demers cartogram allows greater movement in order to preserve continuity between objects and to preserve visual cues.
The New York Times electoral college calculator features a Demers cartogram:
Continuous Cartograms
Gastner-Newman Diffusion Method
I can't say as I fully understand the algorithm, which nevertheless produces very nice continuous cartograms like the following (unfortunately not updated following the 2010 census):
Handmade Continuous Cartograms
A notable feature of types of electoral college cartograms we've seen so far is that they can be computer-designed.
This saves a lot of labor -- designing a cartogram by hand is very time-consuming.
Another advantage is that results are reproducible: two cartographers making a cartogram using the same method will finish with the same result.
However, because these methods rely on machine-computable algorithms, there's no guarantee that the result will be recognizable to its intended audience.
For this reason, it remains possible for a cartogram designer to create a better cartogram the old-fashioned way -- by hand -- than could be created by a set algorithm.
Designers typically apply themselves to continuous cartograms, and typically use a grid as a foundation, with each square representing an electoral vote. Let me point out three handmade cartograms of this type.
Gott-Colley
The Gott-Colley cartogram is prevalent on Wikipedia:
Getty
This cartogram appears on the Getty Images site. They offer this version free to the public, and higher-resolution versions for sale.
Albertson
This is my electoral college cartogram:
I did this by creating a program that allowed me to assign a grid block from one state to another. Just sitting down with a piece of graph paper, a pencil, and eraser, as Gott and the Getty Images designer apparently did, would have been too difficult for me.
I've used this cartogram as the basis for an electoral college calculator, hosted here. These cartograms and others also appear there.
