Working in ArcGIS 10, I have a set of contour lines representing density of commercial square footage, and I have a set of points representing local maxima for each peak of the dataset. For each maximum I would like to find the largest contour line that contains only that maximum and no others.

My strategy is to convert the contours to polygons, spatially join the polygons to the points, choose only the polygons that overlapped 1 point, and for each maximum choose the largest polygon, an operation that will probably happen in MS Access.

I've run into one problem - when I convert the contours to polygons using "feature to polygon", the polygons don't overlap, so my maxima only join to one polygon, breaking the method.

How can I convert polylines to overlapping polygons? If possible, I'd prefer a solution I can fold into an ArcPy script.

  • what do you mean by a set of contour lines, is this one contour layer or more than one? A single contour layer lines should not cross/overlap.
    – artwork21
    Commented Aug 10, 2011 at 11:24
  • 1
    Artwork, I believe he wants the polygons to be complete discs, not rings (no interior "hole"). So even though the source contour lines didn't cross, the resulting polygons would overlap.
    – user3461
    Commented Aug 10, 2011 at 12:39
  • Yes, that's correct. In many forums it seems as though many people have had the opposite problem of trying to convert overlapping polygons to cocentric, non-overlapping ones. (including this particularly thorough one from our own whuber: link)
    – Patrick
    Commented Aug 10, 2011 at 14:06
  • I've accepted whuber's answer, as it gives me exactly what I was looking for, but I think there may be other answers for the general case. Several I had found include using XTools or ET Geowizards to convert the polylines to polygons, or else removing the holes from the non-overlapping polygons.
    – Patrick
    Commented Aug 10, 2011 at 15:44

1 Answer 1


You started off with a kernel density grid. Negate it (thereby flipping it upside down) and fill the sinks. Comparing the filled grid with the original will identify all areas of fill: their boundaries are the desired contours.

  • This is exactly what I needed, and in fact it's much better than what I hoped for. The watershed tool actually gives me exactly the polygons I was looking for in both questions - a polygon that separates the kernel density raster into regions. The method I was attempting here would have only approximated them using the largest contour that only enclosed one maxima, but it would have left gaps. This is perfect. Thank you!
    – Patrick
    Commented Aug 10, 2011 at 15:10
  • @Patrick You have anticipated my answer to your previous question! Since the watershed has worked for you, please consider updating that other thread so others can see your solution.
    – whuber
    Commented Aug 10, 2011 at 15:12
  • This answer perfectly solves my problem from yesterday as well. If you post it there, I will accept it as the best answer.
    – Patrick
    Commented Aug 10, 2011 at 15:14

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