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I have used the aspect tool to visualize the 8(+ Flat) slopes of the different directions, now I would like to get the numbers of the areas for each different direction (+Flat). Anybody knows how that works?

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Of course I would do it via calculate geometry, but it is greyed out even though I'm using the same projection everwhere. –  Daniel May 7 at 10:41

2 Answers 2

The output of the Aspect tool is a floating point grid. Such rasters do not support attribute tables so you cannot count the number of cells for a specific value and there for determine the area.

What you can do is convert your grid into an INTEGER grid using the int tool in the Spatial Analysts toolbox. This will truncate the values to the nearest whole number. The resulting grid will have an attribute table where for each value you have the number of cells. Multiply this count by your cell size and you get the total area within the grid.

But this is no indication of where those values are.

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What about calculating the area sum for each aspect direction? –  artwork21 May 7 at 11:34
    
I'm sorry i forgot to write that i reclassified the data after i used the aspect tool, in that way i was able to get the attribute table, but as i wrote first, i cant calculate a new geometry after i added a new field. maybe there are some ways arround that? –  Daniel May 7 at 12:03
    
The attribute table for the RegionGroup of the integer version of the aspect grid will give the cell counts of each contiguous patch of constant aspect class; multiplying these by the square of the cellsize produces the areas. –  whuber May 7 at 15:45
    
Does it make a difference if I use the Int or the Reclassify Tool?? –  Daniel May 9 at 9:15
  1. Convert float to integer (see Hornbydds' answer)

  2. Make a mask layer for each direction by using raster calculator something like this ->

    con((aspect < xx)|(aspect > xx),1) # true values = 1 (else NoData)

  3. Use extract by mask tool for each direction (use masks created above)

  4. Calculate areas from subsetted aspect rasters(see attribute table)

    • add field "area", set type to double or long
    • calculate area from attribute table by multiplying cell Count by cell area
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flat areas can be calculated from values that are -1. (take this into account when subsetting north slope pixels) –  reima May 7 at 12:15

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