Google Map Maker allows anyone to add map detail in areas of the world where Google Maps at the moment has little data. Check out the two maps of Sri Lanka below. The map on the right is from Map Maker and the map on the left is from Google Maps.
For the sake of accuracy there is often a lengthy delay before the data from Map Maker is added to Google Maps. However Google have now decided to allow map developers to access Map Maker data via the Google Maps API. To add Map Maker data users will have to use the latest 'experimental' version of the API v146b (which means you can play with it but shouldn't really use it as features may be dropped before the version becomes official).
Mapperz has created an example Map of Iceland. Just toggle between the two 'map' buttons to compare Iceland with Map Maker data turned on and off.
Via: Mapperz with a hat-tip to Mike Williams