Teaching Context When it Comes to Map Projections


All maps lie.  The lie is intentional, a compromise stemming from the need to flatten a 3D object onto a 2D surface.  The process varies depending on the map projection but at least one geographic reality, be it area, shape, or direction, will become distorted.  The only way not to incur that distortion, is to keep the representation of the Earth tied to a 3D dimension such as a globe.  Globes, unfortunately, are not so handy to carry around and, even digitally, need to be rotated to see all of the surface.

The rise in easy to use mapping applications has also made the web mercator projection the de facto map projection.  Originally developed in 1569 by the Flemish cartographer Gerardus Mercator, the map projection was developed for seafaring and therefore it preserves angles and shapes needed for navigation.  This aspect made the map projection a beloved one in the early days of web mapping, when driving direction sites such as Google Maps and Yahoo! Maps and MapQuest (remember them?) were emerging. The map projection has stuck and virtually all popular online mapping services use it.  The trade off in the ability to show routes as straight lines has been a distortion in size as latitude increases towards the poles. This distortion is most popularly shown with the comparison of Greenland appearing larger than Africa when in reality the continent is about 14 times larger than the island.

This has triggered the never ending cycle of articles pointing out the injustice of this map projection and was even the subject of part of a West Wing episode.  The latest article about the Mercator projection has triggered a host of criticisms about understanding map projections, with some critics pointing out the irony of rejecting one distorted map in favor of another. The article, published in the Guardian, tells the story of Boston public schools eschewing Mercator projection maps in favor of ones using the Gall-Peters projection on the grounds in a move to highlight accuracy in size over shape. The Gall-Peters projection itself has been the subject of numerous criticisms about its elongated shapes and aesthetic appeal.

Criticisms aside, this article highlighted the need for context when teaching about map projections.  Nigel Waters, a professor emeritus with the Geography Department at the University of Calgary, pointed the way on  CAGLIST to a useful article by David Goldberg and Richard Gott which explains how to use Tissot’s Indicatrix to understand map distortion entitled, “What’s the best map projection?”  The article follows from a journal article published by the authors on quantifying map distortion (Goldberg, D. M., & Gott III, J. R. (2007). Flexion and skewness in map projections of the earthCartographica: The International Journal for Geographic Information and Geovisualization42(4), 297-318.)

The most helpful reaction to the Boston article is a writeup by Andy Woodruff: Your maps are not lying to you. Or, your maps are lying to you but so would any other map.  It’s a good overview of context when it comes to all map projections.  Included is this 1947 animation about “The Impossible Map” which uses a grapefruit to creatively demonstrate why maps distort geography: