(Once again) 2D grid cells over an aerial map

I'm looking for a way to superimpose color-filled grid cells over a
particular area of an aerial map, and there's no need for the grid lines.
Think of it as a map of several communities and you want to lay small
colored tiles over just the area of a selected community to show its population
density or landuse, and leave the rest of the map visible.
Thanks Bill for responding my previous email.
I've looked at the Rivers.java as you recommended but still it doesn't
fulfill my needs which are:
- just colored tiles
- on an image (.JPEG or .GIF file)
- without grid lines

Thanks in advance,

Sitt