So I have lines(road network) and buffers around them. I need to find "empty bufers" whose lines is missing (pic below). Lines have attributes of buffer width, but it is incorrect in some cases (does not match with actual buffer with). So creating/erasing with new polygons is not an option, since it will leave alot of trash polygons. Buffers is also dissolved in most cases.

Example buffer and line

  • I am afraid that in your case you need to choose a tolerance and do the creating/erasing stuff, because you have a dissolved polygon buffer. – radouxju Dec 2 '14 at 7:45
  • How did you get a buffer where there is no line? In any case, @radouxju is correct. You don't have an empty buffer since they're dissolved. – recurvata Dec 2 '14 at 13:06

This is just an idea it would need further experimenting as it may be flawed?

How about looking at some sort of ratio value of length/perimeter?

Imagine you had a line that is 10m long and has its full buffer which you had buffered out by 2m then the perimeter of the buffer would be approximately 20m. so 10/20 = 0.5.

Now imagine you had a line that was 25m long in an L shaped buffer that had been created by a 50m L shaped polyline for which you had only one side of it so giving your scenario of a half empty buffer. You would have a 25m / ~100m perimeter = 0.25.

So values close to 0.5 are polygons with their central lines, would need to test what a good cut off value would be.

Just an idea...


This is just another idea, by looking at the opposite angle to your question, to find centrelines first as explained one of the methods in here and then search for matching line features. Of course this approach will give robust results if the road lines are at the 'centre' of the polygons. Maybe adding thin ('how thin' is another issue of course) buffers to your existing road features, which will introduce a pseudo-tolerance, help you to find similar features by looking at how much of the centreline is 'contained' by the buffer.

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