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I am trying to identify areas of interest in the ocean around 30-150 m that have some "topographic relief" compared to their surrounding areas. I did this manually by looking at the hillshade and circling areas that look like they "bulge out" a little big. However, I know this is not that advanced and was wondering if there was an automated method for detecting relief and creating new polygons from this detection.

I am a beginner.

  • Please take the Tour to better understand how our "Focused question / Best answer" model operates. This question could benefit from a graphic that gives an example. You should always specify the exact release of software in the body of the question. The 10.0 tag indicates software that hasn't been supported in over three years and will likely reduce your response rate. – Vince May 1 '18 at 10:42
  • Teaching computers to "see" things humans find obvious is an extremely difficult task, even for experts. Many of the solutions are likely to be compute-intensive, so specifying the area and map scale is likely necessary. – Vince May 1 '18 at 11:28
  • As has already been said before, a bit more explanation and an image would be beneficial. Like Vince says, this is touching on AI and could require a fair amount of computing power. One option might be to calculate the gradient and then calculate the change in gradient between cells. Then you could see where the change in gradient is greater than a certain value. – Dan_h_b May 1 '18 at 13:39
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From what you have described it sounds like you are looking to identify areas that are perhaps "hilly" in comparison with the surrounding area.

You could try the following - assuming you have access to a "Spatial Analyst" license.

1) Take your surface and multiply it by "-1" in the raster calculator. This will invert the surface, making the valleys hills and the hills valleys.

2) Run the "Fill Sinks" tool ("Fill" in 10.2) from Spatial Analyst -> Hydrology Toolbox. Set the Z-limit to something high, like 100m.

3) Take the Raster created in Step 1 and Subtract the Raster from Step 2.

4) Your output will now be a raster of values greater than 0 ; 0 ; less than 0. Run the Reclass tool assigning a value of 1 to all 0 values and 2 for values which are either greater than 0 and less than 0. Your output will be an integer raster of 1s and 2s.

5) Convert this raster to polygon, then delete all the polygons with a value of 1. The 2s are areas with some type of topography feature.

  • Thanks, but unfortunately I'm not sure it worked (or maybe I did not do it correctly). My bathymetry (called g2m, range -2 - -149) already had negative values only so did this to make a positive one (g2mP). Step 2, I assume you meant "Fill" (there is no "Fill Sinks" in Arc 10.2 but there is a "Sink"). So I ran "Fill" on g2mP and got FillbathP (range 2-140) (should I have done it for the negative one)? Step 3, "Raster calc" my text read "g2mP - FillbathP" The raster I got ranged from zero to 16. When I did step 4, it was basically all 0 values. What am I doing wrong? Thanks. – David Weinstein May 22 '18 at 8:14
  • Ok yes, I see 10.2 has a "Fill" tool. Can you try changing the Z limit to something large, like 100 - or 100m. This will fill the terrain where there is a variation of 100m or less...using this in an inverted topography should fill in the "hills" and show these topographic areas. – Keagan Allan May 22 '18 at 13:10

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