This is a problem that OSM (open street map) has solved. Either use their service, our even create your own clone - their software is likely to be all open source, and their mapping data certainly is.
Nice. I was going to say if everyone is collocated to use a big paper map on a wall. He did say they were "local". Sounds like he's trying to use tech he doesn't really need to solve a problem. But, that's most Ask