Richard: I found this post incredibly useful. Thank you!
Richard Lynch wrote:
...If you only want "close" things to a given location, the curvature of the earth is pretty insignificant.
...
I realized one day that at a distance of a hundred miles or less, I just didn't *CARE* about curvature of the earth, and replaced that trig with your basic Cartesian distance.
Made a *HUGE* difference in performance.
...Put a longitude and latitude column on your existing table, and default it to NULL.
Write your business logic so that *ANY* time a zip code is changed, the longitude/latitude is re-set to NULL. (Or use triggers or whatever you want to make this happen. I don't care.)
Finally, write a cron job (scheduled task in Windoze) to find N records at random in your table where the long/lat is NULL, and *copy* over the long/lat from the zips table.
PPS You can pay $$$ for the "complete" databases of zips, or use the TIGER data for free just interpolate from existing entries to make up long/lats for new zips. EG: If tomorrow the USPS creates zip code 60609, I can be pretty damn sure it's "close enough" to 60601 through 60608 and just average them to make up bogus long/lat. Sure, it's "wrong". It's also FREE and "close enough" for what I (and almost for sure you) are doing.
-- Teach a person to fish...
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