Kenny Evitt already explained the most important things. Nevertheless, here is some additional information:
Postgresql has databases, tablespaces and schemas, and it is impossible to perform joins from one database to another, because they are strictly seperated. One database can have more than one schema, and it is possible to join something from one schema to another. For further information, look at the docs:
Another possibility to load PostGIS in your gc schema would be the following:
t=# create schema gc;
t=# set search_path to gc;
t=# create extension postgis;
I am neither an expert on Arc Catalog nor on pgadmin, but I assume one of the following three possibilities happened:
- Postgresql supports geometric datatypes natively. But you should not trust this in Geo Contexts, because CRS metadata as well as transformation functionality is not given. You just got lucky and nothing broke.
- Arc Catalog somehow, after not finding a PostGIS extension, created it without notifying the User. To check that, you could look at the existing tables before and after that step.
In psql, you can do this by typing:
List of Relations
Schema | Name | Type | Owner
gc | geography_columns | View | postgres
gc | geometry_columns | View | postgres
gc | raster_columns | View | postgres
gc | raster_overviews | View | postgres
gc | spatial_ref_sys | Table | postgres
If you see this, PostGIS has been installed as an extension. The third possibility would be that ArcCatalog does something like this:
set search_path to $all_schemas;
import to gc;
In this case, you also just got lucky. But maybe, ArcCatalog does something more sophisticated in the end...