14. Creating an interactive map

As the Holy Grail of data visualisation, the production of an interactive map is work on data applied to the map of a continent, a country or even sometimes a city. There are basically three main categories of interactive maps: choropleth maps, heat maps and anamorphic maps.

Choropleth maps

This is undoubtedly the most commonly used type of map in the press, most likely because it is the simplest to produce. Choropleth maps allow you to colour the territory of the different administrative entities of a map with a shade of colour according to a given piece of data.

For example, if you want to create a visualisation of the British population broken down by county, the towns with the most inhabitants will be darker and the least populated towns will be paler.

Heat maps

This time, you are not going to establish a colour scale based on a piece of data. The idea here is to indicate, within a database, the addresses, locations or geographical coordinates where something happened. And it is the accumulation of those points that will draw a shape on the map.

One example is the work done in Scotland to identify danger zones for cyclists in the city. Each point represents where an accident occurred. On the map, the accumulation of points indicates dangerous places for cyclists.

Anamorphic maps

In technical terms, anamorphic maps are the most complex to create. In relation to data, they work in the same way as choropleth maps: a piece of data is associated with a geographical area. The difference is that instead of colouring the administrative entity concerned differently, a deformation is applied to it in a software program. Returning to the original example of the British population, the anamorphic map shows the most important population centres within a territory in an instant.