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Land use-counting area(ArcGis 9.2)

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Hi to all!

I have some questions regarding the following issue in ArcGis. I know the basics and I have read many articles and tutorials, however when comes to explaining why to do this and not that it comes the following question:

I want to create map of olive trees of my municipality-actually not by counting the trees, but by counting area (eg. in square m) of its landuse. I have already made the reclassified eleveation, aspect and slope maps from the DEM), which I will use later.

I have the following files, all added to the Table of contents:
- A) digital elevation model 12.5x12.5m of the municipality, (the 32-bit mosaic of 16 grids)
- B) shp file of municipality-outline or border
- C) shp file of different landuses for the same territory (including landuse ID's and its area) The file polygons slightly extend over the border outline (previous .shp file)

Now I want to show all the area of the olive trees (eg the ID for olives is 1230). So one option is to open the attribute table of C) and select by attributes. This way I select polygons. The other option would be to rasterize the landuse, so in the Spatial Analyst I click Feature to Raster (Mask and Extent are both set to B) or municipality outline, while cell size is set to 12.5) and rasterize the Landuse ID column of the Landuse .shp file. I get then cells from different landuses and this way I can calculate area by multiplying the counted cells by its area (12.5x12.5).

My question is - is it right to do so, how accurate it is, or are any other options of calculating the area of olive trees or any other landuse?

I am also confused when instead of Spatial Analyst I use ArcToolbox tools of converting to raster. In this case (trying both "Feature to Raster" and "Polygon to raster") even if I set the Mask and the Extent to the same layer as mentioned previously, the new rasters still extend beyond the outline border, so the mask does not work. So I get different cell count for olives than before. The difference is roughly around 1000 cells.

I apologize for the long post and any help will be appreciated.


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