i've had trouble finding geographical boundaries on neighborhoods in U.S. cities (e.g. downtown areas and residential neighborhoods). anyone know where i can find this?
It's not exactly neighborhoods, but the US Census TIGER database has block and blockgroup boundaries with associated demographic data. You could probably synthesize that into "neighborhood" definitions. http://www.census.gov/geo/www/tiger/tgrshp2010/tgrshp2010.ht...
