The ST_Simplify PostGIS function is able to simplify and generalize either a (simple or multi) linear or polygonal geometry using the Douglas-Peucker algorithm (for more details, go to http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm). Since it can create invalid geometries in some cases, it is recommended that you use its evolved version—the ST_SimplifyPreserveTopology function—which will produce only valid geometries.
While the functions are working well with (multi) linear geometries, in the case of (multi) polygons, they will most likely create topological anomalies such as overlaps and holes at shared polygon borders.
To get a valid, topologically simplified dataset, there are the following ...
