This is not easy in general, especially with parking lots in the image. We can't develop what will have to be a sophisticated algorithm for you and can only refer you to papers that have sucessfully done this already: http://iris.usc.edu/Vision-Notes/bibliography/contentscartog.html#Cartography,%20Aerial%20Images,%20Remote%20Sensing,%20Buildings,%20Roads,%20Terrain,%20ATR See these sections
22.2 Road Network Detection, Road Extraction Systems
22.2.1 Road Following, Road Tracking Systems, Connecting Fragments, Extracting Fragments
22.2.2 Road Network Model Integration, Updating, and Change Detection
22.2.3 Road Extraction in Radar, SAR, Lidar, Laser, Depth