I have a landsat 8 image [UTM 19s] (30m resolution, so 900m sq per pixel). I need to calculate the total area (hectares) from a land cover type. I take the count of pixels from the attribute table, calculate field using the ([count]900).0001 to get total hectares.

As a check, I convert the raster to a polygon and do not simplify so that it returns polygons in a stepped fashion and shaped just like the pixels.This allows me to use the calculate geometry tool to populate an area field. This tool returns different values than the straight calculation from the raster itself. It is off by a few hundred hectares which is far too much for my reporting purposes.

How can I "convince" the two calculations to agree? is one method more precise than the other? I would be inclined to go with the straight conversion from the raster itself rather than relying on the arc tool to produce the areas...Thoughts or suggestions?

closed as unclear what you're asking by PolyGeo Sep 10 '16 at 5:04

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  • Convert from hectares to square meters... I suspect it is a round issue – user681 Oct 19 '15 at 14:11
  • Are the raster image geometrical rectified and are both datasets in the same coordinate system / datum etc.? – Anders Finn Jørgensen Oct 19 '15 at 20:03
  • i converted from pixel size to sq meters to hectares. no rounding issues run into there. the raster is just beign converted into a polygon, it has the same projection as the original dataset. Arc is simply converting from raster to polygon and cant seem to do it correctly based on the actual raster data...it's so strange – mapsmapsMaps Oct 19 '15 at 22:58
  • I think you need to provide more precise descriptions of the steps that you performed to make each calculation, and the results you achieved. – PolyGeo Sep 10 '16 at 5:05