title: Extract building edges from map image using Python
body: <p>I got a map image here.
  I need to extract the edges of buildings for further process, the result would be like step 2 for the post <a href="https://stackoverflow.com/questions/5401661/google-maps-how-to-get-buildings-polygon-coordinates-from-address">here</a>.</p>
  
  <p>Since I am not familiar with this field, can this be done by libraries such as OpenCV?</p>
  
  <p><a href="https://i.stack.imgur.com/fLzI9.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fLzI9.jpg" alt="map image"></a> </p>