Am shyaka from Rwanda.

I use GIS tools and have all required data to perform or calculate surface area from the polygons that have been given by GPS (Trimble) with ArcPad 8.

I originate from a high land region when I map a polygon with different hills, talwegs and when I tried to calculate the surface area using ArcMap in ArcEditor 9.3 just the area becomes too small compare to the decameter.

However, this area does not come from DEM (i.e. I did not use DEM to calculate the area). It is a big problems for me to handle this issue of surface area. I need really your help.

It will be good if you can provide the procedures for how to do this.

  • 1
    Are you interested in calculating the area taking into account topography?
    – Aaron
    Commented Apr 2, 2013 at 11:36

1 Answer 1


I'm having diffulties to understand what you are trying to achieve.

Are you trying to use it for hydrological analysis? I.e. calculating how large the surface is that drains to a given point on what you call a 'talweg'?

If so, R.watershed seems to be what you are looking for: http://grasswiki.osgeo.org/wiki/Hydrological_Sciences I'm no expert on GRASS, but if that's what you need it for someone can probably update the tags on the question. Could be non-hydrological, but what I get from your explanation does sound like it.

Even if it's not - if the underlying mechanics are the same it may be a viable alternative

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