I am just wondering if it is possible for PostGIS to have two geometry columns.
I use shapefile a lot, which has only one "Shape" column for geometry and all geometries in that column has the same geometry type (i.e. POINT, POLYLINE, POLYGON).
I wonder what are the rules for PostGIS regarding the geometry column? Can we have two geometry columns. If so, which is the default when one refer to a row? I've seen the use of
geom some times, are these names required?
I read that PostGIS maintains a view
geometry_columns about geometry columns in tables. The view has a field called
f_geometry_column. I also read that PostGIS takes care of the maintenance of this view automatically. That's what makes me wonder the rules under which it operates.
-- Update --
I have the question because as mentioned above, the way the
geometry_columns view is organized seems to suggest that the correspondence between a table and its geometry column is one to one. Is that right?
Also, if geometry is just another attribute type like Numeric or string, why do we need catalogs like