Originally posted by: mugs
Originally posted by: rnmcd
If not then why are many geographic searches peformed by "distance from zip code"?
"distance from ZIP code" is much more useful if you live in an area where ZIP codes are very small, like cities. With a small ZIP code, the distance will likely be closer to the distance from your actual location. The boundaries aren't really important, since the distance is likely based on the center of the ZIP code.
Edit: As for why they use ZIP codes - you can buy a set of ZIP code data including lat/long coordinates for ~$100. Data for every address in the US would likely be substantially more expensive. Not to mention it's easier to just enter your ZIP code, and your ZIP code is generally sufficient to determine the closest location. The exact distance is not terribly important, an approximate distance is sufficient.