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Extracting data within polygon shapefile

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12-28-2015 01:36 PM
BeckyPerkins
Deactivated User

Hello,

I am trying to determine the percentage of each type of land use within delineated sub-basins. The land use data is in a shape file and the land use types are coded 1-15 and the sub-basins are in a polygon shape file. Is there a way to determine this? I have tried merge, union, join, relate. tabulate area under the zonal spatial analyst tools, etc. The most promising appeared to be the tabulate area tool, but the areas that come out are in unrecognizable units so it is difficult to back check for accuracy.

I would like to have a end result that shows something like:

Area ID     Total Area (ac)    LU1 (ac)     LU2 (ac)     LU3 (ac)     etc.

Area 1        3.25                      0.27             1.64           0.11

Area 2        1.52                      0.33             0.57           0.29

Area 3        5.87                      0.98             1.64           2.00

etc.

Thanks in advance for your help!

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12 Replies
BeckyPerkins
Deactivated User

This is definitely the methodology I want to use. I am still having a units issue, but I assume this goes back to the area being a function of cell size.

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DarrenWiens2
MVP Alum

If you're staying completely within vector methods (no raster), cell size shouldn't be a factor. Calculating areas through field calculator is the "true" area. Cell size is a factor with raster operations that report area based on the count of square pixels (e.g. if the area of one pixel is 100m^2 and the tool reports in units of cell size, if it tells you '5', that means 500m^2, not 5m^2).

As for units issues, confirm that all of your layers are in the linear units you think they are, in Layer properties, Source tab.

BeckyPerkins
Deactivated User

It is actually a user error on my end. The areas that I thought were in acres were actually in square miles which would explain why there was a 640 multiple difference in the image I attached earlier.

Thank you for your help.