http://www.econguru.com/heat-map-of-worldwide-gdp-ppp-per-capita-2008/
This is CIA world Factbook map, each country has different color depth based on their GDP number. High GDP country has deeper color.
Right now, I am considering to develop such effect into my iPhone/iPad map app. I may want to use the apple map (probably not google map since iOS 6 has its own map), but I am not sure how to get such effect based on the country the user visited.
For example, the user visited US the most, then the map shows deeper color in US.
I haven't seen such effect in iPhone app yet. Any suggestion would be appreciated!