title: Is it safe to assume uniform geo-ip resolution for same first-16-bit IP addresses?
body: <p>I have a geo-sensitive webapp for which I send a request's IP to a remote, commercial ip-to-location service, and get back the country, city, ISP, etc. for the IP.</p>
  
  <p>I currently cache the IP lookups in my database in order to make subsequent lookups faster and free (the commercial service charges per lookup).</p>
  
  <p>I wonder if I can further optimize my caching by assuming that the first 16 bits (i.e. the aaa.bbb in a aaa.bbb.ccc.ddd addresss) always have a uniform location. That way I can have at most 2^15 records to cache.
  I don't mind so much about uniformity of ISP but that info would be helpful as well.</p>