[postgis] GEOMETRY_COLUMNS table

Nedjo Rogers nedjo at miningwatch.org
Mon Mar 18 13:11:29 PST 2002

Two questions on the GEOMETRY_COLUMNS table.


The "Type" value in the GEOMETRY_COLUMNS table is limited to POINT,
GEOMETRYCOLLECTION.  However, in polygon and linestring coverages (and, less
often, also in point coverages), particular features may be either single or
multiple.  For example, a polygon coverage is often composed of a mixture of
POLYGON and MULTIPOLYGON type features.  For many uses, e.g., web display,
it would be useful to designate a feature table as being of polygon or
linestring type--without limiting all entries either to single or to
multiple geometries.

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?


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?


Nedjo Rogers

_ _ _ _ _ _ _ _ _ _ _

Nedjo Rogers
Communications Coordinator
Environmental Mining Council of BC
#201--607 Yates St.
Victoria, BC
Canada  V8W 2A7

Phone: (250) 384-2686
Fax: (250) 384-2620
EMail: nedjo at miningwatch.org
Website: http://emcbc.miningwatch.org

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