Filters WKT (Well-known Text) geometries according to their characteristics or geometries using the Contextual Query Language Only the lines for which the expression is true will be kept.

Examples of queries:

• Select entities whom area is smaller than 10 units: "area(the_geom) ≤ 10"
• Select entities whom area between 10000 and 30000: "area(the_geom) BETWEEN 10000 AND 30000"

More examples can be found here: Geoserver CQG Tutorial

Note that the units used in the query depend on the Coordinate System.

The actual processing is done by the powerful geotools library .