The raster functionality in PostGIS has been part of the main extension since it was introduced. When PostGIS 3 is released, if you want raster functionality you will need to install both the core postgis extension, and also the postgis_raster extension.
Many location aware applications need to find things are people that are close to a specific location. The KNN-GiST functionality of PostgreSQL helps developers to create high performance queries to quickly find neighbors, with applications in mapping and proximity searches.
Introduction to Spatial Analytics with PostgreSQL, PostGIS, PL/R and R Programming Language. Demonstration of preprocessing of Geospatial data using PostGIS.