1. GID is just an ID - can be created when you import the shapefile depending
on how you imported it. (discussion
here: http://postgis.refractions.net/pipermail/postgis-users/2007-February/014823.html)
2. ST_Polygonize should build polygons but you might not need/want to (see (5))
3. You should use the SRID of the data that you imported - this should be
stored in a .prj file with the same name as the shapefile. Failing that look
for any other metadata that reveals it (eg. from the data collector's website).
You may be able to "guess" using AsText(the_geom) to see what numbers are
stored.
4. Not necessarily as PostGIS will transform once it knows the CRS, although
you might get interesting results if you mix geometry (plane) and geographies
(geodetic) -see postgis help on Geometry and geography objects depending on the
CRS that you identify.
5. ST_INTERSECTS on point and line will find points that lie on the border
Hope this helps
Phil
>________________________________
>From: rajeev singhal <[email protected]>
>To: [email protected]
>Sent: Saturday, 8 October 2011, 12:57
>Subject: [postgis-users] Query on
>
>
>Dear All,
>
>I imported the US State Border Shapefile data in postgres and on running the
>query :
>select * from us_state_bounds;
>Following columns are returned
>gid id length geometry(MULTILINESTRING)
>
>My query is:
>1. What is the significance of GID Column here (is it just used for sequential
>purpose).
>2. Geometry Column is MULTILINESTRING but i found on googling that Border Data
>is a PLOYGON. How can i convert MULTILINESTRING to
>POLYGON.
>3. Whar SRID should i use. Will default -1 work?
>4. I have a different table that contains point data that i needs to check
>with border data to find which points lie on border. Should both POINTS
>and POLYGON geometry should have same SRID?
>5. For finding the points that lie on border i am planning to use ST_CONTAINS
>function. Is it correct.
>
>Thanks in advance.
>
>
>Regards
>Rajeev Singhal
>
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