She followed that up with another post focusing on one particular factor: the size of the geographic unit. Choropleth maps that shows data by municipality, county, region, state or country will look quite different, even if they show the same data. Averages tend to cancel out extremes. She gives the following examples:
Most of these more common map types focus on a particular variable that is displayed. But what if you have multiple variables that you would like to present on a map at the same time?
Here is my attempt to collect examples of multivariate maps I’ve found and organize them into a loose categorization. Follow along, or dive into the references, to spur on your own investigations and inspirations!
Jim’s examples of maps that display more than one variable include 3D maps, multicolour choropleth maps, multiple small maps, and embedded charts and symbols. Useful and enlightening.
Will Geary’s TransitFlow project is an experimental set of tools to build animated transit flow visualizations, built from Transitland’s open-source transit schedule data. More than a dozen visualizations are available in video form here; each shows the flow of trains, buses and other forms of transport over the course of a day. Very high visual appeal. More at the Guardian. [Metrocosm]
Speaking of National Geographic. If the magazine is known for its cartography and its photography, one should not forget the illustrations, charts and infographics that accompany many of the articles and appear on the back of every folded map that comes several times a year with a magazine subscription. Now there’s a book of them: National Geographic Infographics. Edited by Julius Wiedemann and published by Taschen, the book “gather[s] the magazine’s best infographics of the past 128 years.” More at Atlas Obscura and Wired.
This interactive map shows the location of every single cargo ship over the course of 2012. Shipping routes (the Straits of Malacca look particularly bottlenecked) and materials shipped are available via the interface, and there’s a nice narrated tutorial explaining how the map works. Thanks to David Krathwohl for the tip. [Digg]
The Ordnance Survey has created a series of data visualizations showing the most popular walking and cycling routes, based on OS Maps usage. “The 500,000 plus routes were illustrated in a series of beautiful data visualisations by [cartographic designer] Charley [Glynn], who found itamazing that the people who created routes for their outdoors adventures had logged almost every bit of British coastline. It neatly frames the rest of the data and gives the illusion you are looking at a map of Great Britain. The darker, thicker areas illustrate the higher concentration of routes and reveal popularity.” Flickr gallery. [Mountain Bike Rider]
The Washington Post’s Christopher Ingraham compares two choropleth maps of U.S. population growth: while they look rather different, they use the same data. “The difference between my map and Pew’s—again, they both use the exact same data set—underscores a bit of a dirty little secret in data journalism: Visualizing data is as much an art as a science. And seemingly tiny design decisions—where to set a color threshold, how many thresholds to set, etc.—can radically alter how numbers are displayed and perceived by readers.” [Andy Woodruff]
(Worth mentioning that this is exactly the sort of thing dealt with in Mark Monmonier’s How to Lie with Maps.)