CompuServe Messages

Forgive me for barging in here, but I've been researching a problem you may be able to help solve. The problem is this. Suppose there are two or three thousand individuals carrying GPS receivers around the country. Their mission is to inspect manhole covers. Also, suppose there are millions of automobiles, each with a GPS receiver, passing over manhole covers. I want the frequency with which automobiles pass over manhole covers (should I be calling these person-hole covers? Anyway…). If I assign, from a pallet of 255 colors, the range of possible frequencies, and bring up a map of the US, I should see various colors indicating the information I want. Question #1: Is there a current source for the lat/long of manhole covers? Question #2: Is there a current package that allows me to plot values by lat/long, over a map? Any suggestions would be most welcome. Thanks. David Stuart.