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What is the easiest way to check if z values of contour lines are correct in ArcGIS?

I need just to look at the values, to see if equidistance between them is correct and unchanged.

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2 Answers 2

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For many contour maps a check of spatial consistency among the contour levels is not possible unless you supply additional information. Here's an example pulled arbitrarily from Google Images:

enter image description here

The criterion for consistency is that the neighboring lines of each contour line should have values differing by at most one contour interval. But if you draw a line segment from the eastern terminus of the 4.0 contour to the eastern terminus of the 4.8 contour, this segment will not intercept any other contour line: thus the 4.8 line is also a "neighbor" of the 4.0 line, even though it is two intervals away. To cope with this problem you need to specify the region being contoured. In this example, it's the polygon bounded by the thick cyan curve.

Assuming you have specified this region as a polygon, then one of the easier ways to do the consistency check is to press Spatial Analyst into service to perform a Euclidean Allocation calculation of the contour lines, using the region polygon as a mask. This expands all lines until they meet their neighbors, but it does not allow the expansion to extend beyond the mask. At any meeting point, only two contour levels will be involved (otherwise you do indeed have a problem!). (You can verify that only two levels ever meet, by computing a focal variety grid and checking that its maximum value is 2.) If you compute a 3 x 3 focal range of the Euclidean allocation grid, it should therefore equal either zero or the contour interval (assuming the interval is constant). That is extremely easy to check by looking at the attribute table or histogram of the focal range grid.

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What are you comparing them against? Do you need to just look at the values or you need some sort of verifyable solution (testing against a MDT).

Your question is too generic, please, detail.

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1  
Perhaps you could reformulate this as a comment. –  whuber Mar 26 '11 at 22:42
    
I need just to look at the values, to see if equidistance between them is correct and unchanged. –  againstflow Mar 27 '11 at 14:03

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