PostGIS adds support for geographic objects to the PostgreSQL
object-relational database. In effect, PostGIS "spatially
enables" the PostgreSQL server, allowing it to be used as a
backend spatial database for geographic information systems
(GIS), much like ESRI's SDE or Oracle's Spatial extension.

To disable raster support and eliminate the gdal dependency,
set RASTER=no. If you choose this path, be aware that
postgis will still need the two dependencies that gdal
rely on, proj and geos.