[postgis-users] -- Still having trouble retrieving properties 100 meters around a point --

[Greg Troxel]

I'm new too, but I think you should omit the latitude/longitude
columns and instead simply have a geometry column (which will have
lat/lon in it); the examples in the manual are all like that and the
point of postgis is to make lat/lon be something that's understood by
the db so the spatial operators can work.  Having redundant values
means it's more work and (less certainty) to have them consistent, or
it gets you into adding contraints and update triggers when it isn't
necessary or useful to do so.

For reference system, the real question is what datum the data you
have is in.  For country-wide use the choice of a datum tagged as NJ
specific is almost certainly inappropriate.

For the US, and given data in lat/lon, the three likely choices are
  NAD27 CONUS
  NAD83
  WGS84

For mapping, NAD83 and WGS84 are essentially the same (meaning
differences are below the accuracy of your data).  NAD27 and NAD83
differ significantly.  Odds are good that you should just use WGS84,
but ask your data provider which datum.  If they don't know, you have
a problem, but in that case picking WGS84 is probably 80% likely to be
correct.

-- 

    Greg Troxel <gdt at ir.bbn.com>
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