title: Heat map from latitude & longitude
body: <p>I want to generate heat map from a set of data which is latitude &amp; longitude. I've 20,000+ latitude &amp; longitudes in a text file. </p>
  
  <p>Can any one tell me how to generate heat map? </p>
  
  <p>I'll appreciate if some one can provide me free version of heat map.</p>
  
  <p>Thanks!</p>