Google Map maker is now available for you and your peers to add, edit and moderate most features you see on maps including roads, lakes, parks, points of interest, businesses, cities and localities. For a large area, you can divide it into small area so that you can work with your part and let the others to do their parts and merge them together once finished.

Google Map Maker lets people add details to maps in some countries.

(Credit: Google)

Reference: http://news.cnet.com/8301-10784_3-9976423-7.html?tag=bl