Postgres: http://www.postgresql.org/docs/8.1/static/indexes-types.html http://www.postgresql.org/docs/8.1/static/indexes-types.html: "PostgreSQL provides sever

Postgres: http://www.postgresql.org/docs/8.1/static/indexes-types.html http://www.postgresql.org/docs/8.1/static/indexes-types.html: "PostgreSQL provides several index types: B-tree, R-tree, Hash, and GiST. R-tree indexes are suited for queries on two-dimensional spatial data." PostGIS: http://postgis.refractions.net/ http://postgis.refractions.net/ : "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)" Also see "Programming the K-means Clustering Algorithm in SQL": http://pdf.cx/6gc9a http://pdf.cx/6gc9a