Detail view of two sets of neighborhood boundaries in San Francisco. Data from sfgov.org and zillow.com

Mapping the boundaries of neighborhoods is difficult. The notion of a neighborhood is a mixture of indivduals' and groups' concepts of socially defined locations. Combined with the cartographic need to define a specific location for a neighborhood boundary, the fluid definitions of neighborhoods create ample opportunity for discussion. There are more than a few resources for neighborhood boundary files for use in GIS software:

Flickr Alpha Shapes

Shapefiles available through the Flickr API.

Zillow Neighborhood Boundaries

Shapefiles of neighborhood boundaries for the largest US cities licensed under a Creative Commons license.

City of San Francisco GIS files

Neighborhood boundary files from the City of San Francisco. Users must register, for free, to download data.

UK Ordnance Survey Location Lingo

A project to create an alternative placename gazetteer via the OS Open Space API.