I am trying to make a polygon of the boundaries of traffic intersections using a python script. I want to automatically create intersection polygons made of arcs and lines connecting them. Essentially, what I need to create are lines labeled in red below to finish off the polygon.

How do I make the script "know" which two arc endpoints to connect to make the red lines? If I create a line between each point and its nearest neighbor, it could mess up if one road is wider than the other. Also, how could I make the line extend perpendicularly from the ac endpoint until it hits the other end of the intersection? enter image description here

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    Are there road name attributes? Road A could be going East-West, and Road B could be North South. Then, you could use the name of Road A and B to link them. You know the end points of Road A need to match with Road B. Alternatively, you could get the endpoint coordinates and sort them clockwise, for example. Then connect them in order. – Fezter Aug 3 '16 at 22:25

Here is an approximation assuming that you have individual lines representing your roads:

  1. Buffer your road lines
  2. Intersect the buffered polygonsenter image description here

The result should look approximately similar to the picture below:

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