title: Maximum length of a decimal latitude/longitude Degree?
body: <p>What is the maximum length (in kilometers or miles - but please specify) that one degree of latitude and longitude can have in the Earth surface?</p>
  
  <p>I'm not sure if I'm being clear enough, let me rephrase that. The Earth is not a perfect circle, as we all know, and a change of 1.0 in the latitude / longitude on the equator (or in Ecuador) can mean one distance while the same change at the poles can mean another completely different distance.</p>
  
  <p>I'm trying to shrink down the number of results returned by the database (in this case MySQL) so that I can calculate the distances between several points using the <a href="http://en.wikipedia.org/wiki/Great-circle_distance" rel="noreferrer">Great Circle</a> formula. Instead of selecting all points and then calculating them individually I wish to select coordinates that are inside the latitude / longitude boundaries, e.g.:</p>
  
  <pre><code>SELECT * FROM poi
   WHERE latitude &gt;= 75 AND latitude &lt;= 80
     AND longitude &gt;= 75 AND longitude &lt;= 80;
  </code></pre>
  
  <p><strong>PS: It's late and I feel that my English didn't came up as I expected, if there is something that you are unable to understand please say so and I'll fix/improve it as needed, thanks.</strong></p>