Modern databases shine not only at data storage and retrieval, but also data processing. The set of statistical and mathematical functions in pure PostgreSQL is impressive. In PostGIS, the same principle applies to spatial data. A wide array of geoprocessing functions is at the database user's disposal, and all these functions can be called from within SQL statements. In this chapter, we will discuss the processing capabilities of PostGIS referring as regards to common GIS operations. Those operations include the following:

• Merging and splitting geometries
• Buffering and offsetting geometries
• Computing polygons' centroids and point-on-surfaces
• Computing the difference of geometries
• Reprojecting geometries
• Querying features based on their spatial relationships