Zip codes are mainly for the US postal service, towns are a better way to go worldwide.

Proficiently doing towns in the world would require a well designed database and an optimized script because you would be working with tons of different locations and you have to compare them against each other (a good narrowing algorithm would be required).

I would stick to zip codes for now, but having something that could do a good portion of the world would be an awesome project to take on. As wild put it though, zip codes are just a way to reference to the GPS, so you could easily use the same theory to power a town based search.

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