[postgis-users] Latitude and longitude distances

[Ethan Alpert]

> ... your reference location was (80.5W, 40.5N).  Then to 
> retrieve all rows in a 3-degree radius of you reference, ...

See that's the problem. The applications of a 3 degree radius are very
limited. For my work I need to deal in meters. Using degrees is
problematic because a 3 degree radius buffer for instance varies in
"real world" size by a function of the cosine of latitude. Unless your
data is highly localized and at mid latitudes you are not filtering on a
constant "real world" size. This was my original point so the approach
one takes must be chosen by the requirements of the application at hand
and can (should) not be used in a generic sense.

-e