Are there any additional locations for obtaining Longitude and Latitude values for zip codes) or is there an authoritative source for the data within the zips.csv file that is downloadable?
Here is what it says in the readme file that comes with the SQL data:
All zip code information was taken from the U.S. Census Bureau's 2000
Gazetteer files. They can be found here:
I just used this in a project of mine and out of about 1500 records I was missing about 20 ZIP codes so I added them to my database using this process:
1 - I typed the ZIP code into Google Maps. If it's a good ZIP code, you'll get a map with the ZIP code still in the search field but you'll probably also see a town name in the search result.
2 - Chose 'What's here' for the map marker that Google made; the search window will now show the lat/long.
3 - Copy/paste that lat/long into the new database record along with the town name.
I don't know exactly how the lat/long was figured by the census folks and they pretty much disavow accuracy of anything to do with ZIP codes since they change so much. I figured this approach was good enough for my purposes.
It would be nice to keep a supplement database available on this site, but I guess we would all have to register as developers and use SVN or something?