svdiomedea

Area tabulated under fishnet incorrect

Discussion created by svdiomedea on May 13, 2014
Hi,

I have a raster layer over which I have laid a fishnet grid 14 x 14.  Under each fishnet polygon I have used Tabulate Area to calculate the proportion of each raster value in that cell.  The problem is that when I export the data to excel and sum all of the values within each fishnet cell, I get a repeating pattern of cells with lower values as follows:

1   20220.84000000000
2   20220.84000000000
3   20220.84000000000
4   20220.84000000000
5   20220.84000000000
6   20220.84000000000
7   20220.84000000000
8   20220.84000000000
9   19097.46000000000

After this point, I get the same value for the following 13 cells (20220.84000000000) and different value in the 14th cell (19097.46000000000).  Then at cell 113 I get 14 sums of the smaller number (19097.46000000000 ) before returning to the same pattern as in the beginning.

I have repeated this process with 8 different rasters and I get the same exact pattern for each of them.  This cannot be an issue of overlapping polygons because the fishnet polygons do not overlap.  The extent of the fishnet was set to the extent of the raster. I have checked the rasters and there are no missing values.  This is approx. a 6% error which is large enough to be of concern in the analysis I am doing.  Is this a bug?  Or am I doing something wrong?

Thanks

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