How do I convert a latitude/longitude pair into a PostGIS geography type?

Question

I'm trying to load a bunch of latitude/longitude pairs into a PostGIS geography type so as to be able to query by location.

In particular I have a table with float latitude and longitude columns and a geography(Point, 4326) column. I would like to do

update mytable set geography = ???

The documentation appears to suggest that the following should work:

update mytable set geography = ST_GeogFromText('POINT(' || latitude || ' ' ||
                                                           longitude || ')');

It doesn't. I don't know what it's interpreting this point as meaning, but it only allows the longitude to lie between -90 and 90, so it's clearly not a longitude.

So, what do I do?

Answer 1

...sigh. Stupidity on my part. Apparently the correct order is longitude, latitude. I was fooled into thinking that both coordinates had the same range (-180 to 180) so thought something more subtle was going on.

Answer 2

Thank you, Evan!

I kept getting the following error in Django using GIS/GeoDjango:

DatabaseError: Coordinate values are out of range [-180 -90, 180 90] for GEOGRAPHY type

It turns out the problem was exactly what you described. With geometry fields, the point field was formatted POINT(LAT LNG), but with geography fields, it's POINT(LNG LAT).