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How can I find depression contour lines? I already have find depressions via Fill-method, but now I try to detect them by using the contour lines, anyone have an idea ?

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2 Answers

This ESRI blog post describes a method for finding depressions using contours. On a topo map depressions look like this:

enter image description here

Note that the above approach is not desgined to be programmatic, but simply relies on symbolizing the contour lines using different colors so that you can visually find lines which do not fit the pattern of stepwise increases.

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thanks for your answers :), but I'm looking for a automatic/programmatic approach –  Tobi Apr 22 '13 at 12:30
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My opinion is the vector/contour lines are more appropriate for a visual inspection, whereas your original raster is more appropriate for programmatic inspection. Having said that, however...

You might try doing a definition query for the shortest contour lines. As this would designate smaller perimeter measurements, which should be a trait shared by depressions. Of course this will require a heuristic to establish the maximum acceptable length for contours that signal depressions.

If you have a few known depressions---on the ground---that you can measure corresponding contour lengths for in your GUI, you could establish a quick and dirty rule just for the sake of testing the concept.

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The shortest contour lines will, in general, mark peaks. Looking at length also risks including pieces of contour lines typically found near edges and corners of maps. Another disadvantage of using length is that contours in rugged regions will tend to have longer measured lengths than contours covering the same areas in less rugged regions. All in all, selecting depression contour lines based on length does not seem a promising approach. –  whuber Apr 17 '13 at 18:31
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If you would like to think about this further, I would suggest converting all contour lines to polygons and studying the structure of their inclusions. A depression contour is one whose polygon is included within the polygon of a contour having higher elevation. (This is a simple, rigorous, correct characterization.) There are various ways to make this characterization operational, such as (the inefficient but easy one of) performing all pairwise comparisons of the polygons. –  whuber Apr 17 '13 at 18:34
    
Ah. I suspected this question might not get any attention so I wanted to offer the one thought I had. I know for sure I've seen depressions visualized on topo maps using hashes against the contours, so I thought a lengths comparison might work. Thanks for providing these contrasting insights. –  elrobis Apr 17 '13 at 18:44
    
Thanks for your reply and you approach. At the moment, my idea is to find all contour lines without a smaller neighbor on the right-side(inside the contour line), but I have same problems to detect them . I know there is a possibility in Arcgis Desktop Advanced (Polygon Neighbors (Analysis) ). –  Tobi Apr 22 '13 at 11:47
    
Just been thinking about whubers answer, I bet you get some wacky topology. I was just thinking of the scenario of a volcanic caldera such as Mount Teide where the rim is higher, drops down to a plateau then peaks again with the central cone. So you have a peak inside a depression contour! Just thinking aloud... –  Hornbydd Dec 23 '13 at 13:44
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