What is the most complete, precise and reliable way to get the coordinates (latitude / longitude) of a given ZIP / Postal Code of a given country? I need to make a lot of requests, so a high API limit rate (maybe even absent) would be useful.
GeoNames dumps would be cool, but it seems to have way too many duplicate coordinates (example) and it also seems that their database is missing some ZIP / postal codes for specific countries.
Are there any other (reliable) alternatives?
While I was reading a Meta question, I came across this link:
http://query.yahooapis.com/v1/public/yql?q=select%20%2A%20from%20geo.places%20where%20text%3D%22Jyv%C3%A4skyl%C3%A4%22&format=xml
I had heard of the YQL before but I had no idea I could use it to GeoCode addresses, so I searched a little and I found this very interesting piece of information:
Usage Limits
Per application limit (identified by your Access Key): 100,000 calls per day
Per IP limits: /v1/public/: 1,000 calls per hour; /v1/yql/: 10,000 calls per hour
Does anyone know where I can get more specific info in using YQL to GeoCode addresses?
Yahoo! GeoPlanet will give you centroid lat/long points for postal codes. They've been reliable in my experience. The API limit is 50,000 requests per day. I'm not sure what their policy on caching results is. I get the impression that if you contact Yahoo!, you can set up an arrangement with a higher request limit, though it may cost some money.
They also let you download a substantial portion of their data under a Creative Commons license, but unfortunately that appears to be limited to the WOEID relationships and country names.