title: how to separate coordinates to groups of nearby coordinates
body: <p>I have coordinates (lattitude and longitude) of some cities and I want to create groups of nearby cities. You can see illustration:</p>
  
  <p><img src="https://i.stack.imgur.com/9H7Z6.jpg" alt="Grouped coordinates"></p>
  
  <p>Do you know some tips, how can I do it?</p>