title: How do you ID GeoHash points that are NOT over land?
body: <p>I have a list of coordinates in latitude/longitude that I have converted to GeoHash.  My goal is to ID the points that are reported to be over water (oceans, seas, etc. outside of any countries borders).  I also have a data set of all the shapes of all the worlds countries borders in latitude/longitude converted to GeoHash too.  </p>
  
  <p>So for a given GeoHash point I am trying to be able to classify it as being over (international) water or not.  I thought about picking points manually in the middle of the ocean and using a short GeoHash prefix to create a large box in the ocean but that is fairly limited.  </p>
  
  <p>Perhaps generally there is a way to understand what it means to be a GeoHash point outside of any countries borders?</p>