5.4 Proportional symbol maps

Proportional symbol maps, or more often proportional circle maps, associate a particular symbol, typically a circle, with a particular point on a map, such as the centre of a city, or the capital city of a country. The diameter of the circle represents some function of the quantity being visualised.

For example, the proportional symbol map in Figure 15 depicts the number of internet users per country in 2007 (data source CIA World Factbook; map produced using Many Eyes).

Figure 15 Proportional symbol map of the number of internet users per country (2007)

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Here a screen image of a world map is shown with brown dots of various sizes scattered over the map. The dot with the largest radius is on the USA and the next largest on China. There are some medium-sized dots on India, Japan and some European countries with slightly smaller dots on the rest of the world. At the bottom left a key explains that dots represents millions of internet users per country. The largest dot represents 150 to 180 million users and the smallest 0 to 30 million.

Figure 15 Proportional symbol map of the number of internet users per country (2007)