PostGIS adds support for geographic objects to the PostgreSQL object-relational database. In effect, PostGIS "spatially enables" the PostgreSQL server, allowing it to be used as a backend spatial database for geographic information systems (GIS).
JOSM goes multi data layer July 18th, 2007 The latest JOSM now supports multiple data layers again. This was requested since about the day after I removed the feature over a year ago ;-) . As another big data source hits the main database (AND’s nethe
Contains various map databases on topics including topography, biodiversity, water use, etc. Also contains links to other GIS data sources. A good starting point for searching for GIS data from the United States.