Posts tagged with 'geography'

pgAdmin shows no data

Every one or two months, someone asks on the PostGIS users list usually somewhat panicked, My geometry is missing when I look in pgAdmin III

This is documented in the PostGIS Frequently Asked questions section of the manual I tried to use PgAdmin to view my geometry column and it is blank, what gives?

Since this question gets asked so much, I thought it best to highlight it again.

Spatial objects can be big things and if your geometry, geography, or raster row field is big enough, pgAdmin is not going to load it and will just show an empty field. This is by design. There are a couple of ways to verify you really have data and even how big your geometry, geography or raster column is

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Distance proximity: Use ST_DWithin not Distance

If you have a problem that involves finding the things within X distance of other things or finding what things have nothing within X distance do not use ST_Distance for filtering and also do not try to use ST_Intersects + ST_Buffer.
Use ST_DWithin instead. Why?

  1. ST_DWithin can use an index and ST_Distance can not

  2. ST_Buffer is just an approximation of a buffer and not an exact buffer

Also note that ST_DWithin is supported for both geometry and geography.

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Is it Lon / Lat or Lat / Lon?

In mapping frameworks spatial coordinates are often in order of latitude and longitude. In spatial databases spatial coordinates are in x = longitude, and y = latitude.

If you accidentally loaded data as lat,lon, you can always fix the mistake by using the ST_FlipCoordinates function introduced in PostGIS 2.0.

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