cyanblue the technology is calles Geographical information systems (GIS), its been around for ages, arcinfo and arcview being the two best known examples.
you can get quite a bit of GIS data for free from esri, local councils, goverments to name but a few. also postgreSQL 8 supports GIS data natively now (just shapefiles and their associated dbf files) so doing a real mapping job is now cheaper than 2 years ago.
for some more info.
this is a hobby of mine in the freetime, since half my familiy are planners and geographers