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I have an IDW, tension spline and hill-shade rasters that show an archaeological landscape and from these rasters I want to identify new features which are seen in the landscape as depressions. And from this raster I want to calculate the size and shape of these features. I have not yet come across a form of analysis that would do this, or I am just not understanding the different types of analysis I have looked at.

I have been using GRASS, QGis, ArcMap/Secne and surfer, but I'm willing to give anything a try.



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Christina, take a look at curvature analysis. There is a nice discussion of curvature in this thread: How to calculate terrain Curvature. In GRASS it is available in r.slope.aspect and r.param.scale. ArcGIS also has a Curvature model. I would highly recommend using r.parm.scale because it will allow you to vary the size of the window that curvature is calculated whereas other methods are limited to a 3x3 window. Once you have a curvature surface you should be able to find a threshold that will allow you to classify your depressions and calculate size/shape.

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