Ed. This text was originally published as the introduction to Cities Squared: Making Urban Data Legible.

Data provides solutions to the most pressing challenges that cities face in the 21st century. Advances in data technologies mean that city managers can capture rich data associated with transport, pollution, and social mobility. But how can we visualise this data, and tell stories with it? How can we use maps to tell these stories?

There have been advances in digital display technology for geospatial data, making it much easier to plot urban data on maps. However, most city maps still remain faithful to real-world geographic scale (or at least given the impression of doing so — all maps transform the world they represent in some way). The issue with geographical fidelity is that lay map-readers tend to conflate size with importance. For example, the public tended to misread maps associated with US elections and the Scottish independence referendum, where large but sparsely populated voting districts seem more important than smaller, but more populous districts. We sought to solve this problem by using “equal-area cartograms” — maps in which all districts are made the same size, meaning each district has the same visual weight (we will refer to these cartograms hereinafter as “square maps”). Square maps are usually only used to represent countries or continents — no one makes square maps of cities. This is partly because there wasn’t always so much data on cities, but also because reporting tends to look at larger, national or supra-national patterns. Today there is a lot more granular city-level data available. …