How to guard spatial data quality using constraint triggers and spatial relationships.
Constraints are used to ensure that data in the database reflects the assumptions of the data model. Paul Ramsey demonstrates simple and complex constraints that spatial database users like to enforce on the geometry data.
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.