Mastering PostGIS

Creating an empty topology

After installing the topology extension, one more preparation step is needed before we can work with data: a new, empty topology has to be created. There are two functions for this: topology.ST_InitTopoGeo and topology.CreateTopology. The former is defined by the ISO standard, and accepts only one argument: the topology name. The latter is a non-standard version that allows the definition of additional parameters: the snapping tolerance, SRID, and dimensionality. Let's use the non-standard version:

SELECT topology.CreateTopology('my_topology', 4326, 0.00028, FALSE); 

The first argument defines the topology name, the second is SRID (in this case, WGS84), the third specifies the precision (in this case, 1 arc-second, ...