[postgis] GEOMETRY_COLUMNS table

Paul Ramsey pramsey at refractions.net
Mon Mar 18 13:15:44 PST 2002

Nedjo Rogers wrote:

> To use polygons as an example: Is it necessary to use GEOMETRYCOLLECTION
> when a coverage may contain either single or multiple polygons, or is it
> acceptable to put merely "POLYGON" as the type?  If POLYGON doesn't work,
> could there be some other solution?

Use MULTIPOLYGON. ESRI Shape polygon files, for example, are all
multipolygons. A single polygon is easily represented as a multipolygon
with a single element. No problemo.

> For many purposes, it might be desireable to track layer information in
> addition to that included in the GEOMETRY_COLUMNS table.  For example, a
> particular application might call for a minimum and maximum display scale.
> These data could be added as extra fields to the GEOMETRY_COLUMNS table, or
> they could be included in a new table (e.g., with a one-to-one relationship
> with the GEOMETRY_COLUMNS table based on F_TABLE_NAME).
> Is there a strong reason to pick one option or the other?  Is the
> GEOMETRY_COLUMNS table best left as it is?

I would be interested in people's opinions. Once you start down this
road, the complexities never end. Prefered fill and outline colors,
scale preferences, full descriptive names. Is the storage of this
information necessarily a part of the backend data store, or should it
be part of the rendering application solely? The only benefit to pushing
it back into the database is that applications can then share rendering
specifications: to make my roads blue on both desktop and web apps, I
change it once in the database. 

My tendency is to think that rendering preferences should be stored in a
manner specific to the rendering tool. If the rendering tool is specific
to PostGIS, then fine, store the specs table in the postgresql database,
but not as a part of GEOMETRY_COLUMNS. Other thoughts?

     | Paul Ramsey
     | Refractions Research
     | Email: pramsey at refractions.net
     | Phone: (250) 885-0632

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