Vector-based GIS, if not by definition then de facto, are organized around databases of geographic objects, storing their geometric definitions, geographic metadata, object relationships, and other attributes. Postgres is a leading open source relational database platform. Unlike SQLite, this is not a file-based system, but rather it requires a running service on an available machine, such as the localhost or an accessible server. The spatial extension to Postgres, PostGIS, provides all the functionalities around geospatial data, such as spatial references, geographic transformation, spatial relationships, and more. Most recently, PostGIS has come to support topology—the formal relationships between geometric objects. pgRouting is a topological analysis engine built around optimal path-finding. Conveniently, PostGIS now comes bundled with pgRouting. The following content applies to Postgres 9.3.