This is interesting -- it's a map of vehicle CO2 emissions by municipality in Japan.
Here's how they calculate the data:
The CO2 vehicle emissions shown on the map use estimated emissions figures by municipalities nationwide, calculated using an estimation method by NIES based on the Origin-Destination Survey data of 1999 and 2005 road traffic censuses. Clicking on the map for "emissions per person" reveals figures for calculated annual emission volumes from passenger cars, freight vehicles, and the total number of vehicles. The same information is shown for "total emissions."
More information can be found here:
http://www-gis5.nies.go.jp/carco2/co2_main.php (Available in Japanese only)
The National Institute for Environmental Studies (NIES) official website