[GRASS-user] grass topography and postgis

[Markus Neteler]

On Tue, Dec 2, 2008 at 11:12 AM, Matt B <mattslists at gmail.com> wrote:
> Hi Markus,
> I possibly don't have a full understanding of what topology is. I thought it
> was more or less the geometry, with a few rules relating different objects
> to each other.

Inofficial definition, without reflecting too much about it:
- Geometry is the geometry (primitives like points, lines, boundaries,
centroids etc).
- Topology is the relationship between these primitives.
- Attributes are values/descriptions logically attached to the geometry (in
     GRASS, the cat column is used for that, cat is also stored in the
geometry).

In topological GIS (eg GRASS) common boundaries are shared while in
non-topological GIS (eg ESRI, PostGIS,ok that's no real GIS) they are not,
obviously leading to more work to keep data consistent (i.e., avoid slivers
and gaps).

Markus