[postgis-users] Storing Points and Polygons

Brent Wood pcreso at pcreso.com
Tue Dec 18 04:31:23 PST 2007


--- Max <postgis at lists.meisel.cn> wrote:

> Hello,
> 
> because i`m a newbie to postgis i`ve got a question related to storing
> point and polygons. Do i have to store points which are included in more
> than one polygon, redundant?
> 
> For example: i do have two polygons:
> 
> POLYGON(1 1,1 2 ,2 2 ,2 1,1 1)
> POLYGON(1 1,1 4 ,4 4 ,4 1,1 1)
> 
> in both polygons point(1,1) is included. So if i want to change the
> coordinates of that point i have to change it in all polygons or can i
> just have a table with points on one with polygons which refer to the
> point?


What you are asking about is a topological GIS, where features are built up
from other features, and can share arcs, etc.....  PostGIS does not currently
support this functionality, although it has been discussed here before. PostGIS
supports the OGC Simple Feature Spec, which is non-topological, so at present
you'll need to modify all instances of a point or arc common to more than one
feature separately.

The snapping functionality of GUI PostGIS editors such as QGIS may make this
process easier, as you can move one vertex, then snap the others to the same
location.

Cheers,

   Brent Wood





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