You are not limited to just using static data in your spatial analysis. You can also create new geometries and manipulate existing geometries directly within a PostGIS database. While it's easy to create a brand new geometry using functions such as the
ST_GeogFromText() function we used earlier, you can also use the PostGIS geometry editing and geometry processing functions to create new geography values derived from old ones.
There are some limitations on the functions available when you use the PostGIS
GEOGRAPHY type. PostGIS originally only supported the
GEOMETRY data type, which was designed to only work with spatial data projected onto a flat Cartesian plane. When using the
GEOGRAPHY field, check the PostGIS manual ...