Re: Radius of a zip code

"tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane)" wrote in comp.databases.postgresql.sql:

[sNip]
> I'm guessing that the big problem is that you didn't measure longitude
> and latitude in identical units in your table, so your "circle" isn't
> real circular, and the smaller problem is that "miles" converts to
> "degrees of arc" differently at different latitudes.

Don't forget that there are two different types of "miles" which need
to be considered when measuring distances:

1 statute/land mile = 1.609 km
1 nautical/sea mile = 1.85 km

Since kilometers are consistent over land and water (and in the great
vacuum of space), the metric system should always be used to ensure clarity,
unless the only land masses the user is concerned with have no bodies of
water.

=)

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