In a previous blog post, I demonstrated the new thematic map feature of the Google Chart API. I was not too impressed with the choropleth map it returned. A greater advantage of this API is the possibility to put charts on top of web maps. I here demonstrate how this can be achieved using OpenLayers.
This map shows the total population and the age distribution in each country of the world in 2005. Instead of proportional circles, I’m here using pie charts to symbolise the population. The chart size is mathematically scaled in direct proportion of the total population. The pie chart itself shows the age distribution as shown in the right figure.
There are some performance issues since about 200 pie chart images have to be downloaded for each zoom level. Even though Google recently removed the limit on the number of daily requests, I guess they’re not too happy with this way of utilising the API…