0

I have a rasater data with cell values of the following: missing, 1, 2, 3, 4, and 5

Now I need to find the fraction defined as (area with value 5)/(Sum of areas with values 1,2,3,4) for a certain polygon.

So I need to ignore missing values.

How do I do that in Arcmap?

Improve this question

1 Answer 1

Reset to default
1

Your operations will ignore missing data anyway.

So each cell has an x and y resolution. So you know the size of the cells. This is constant across the raster (almost always).

Just just calculate the count of cells with 5 in a polygon and store this in the polygon. This is merely the count value in ArcGIS for an integer raster. Call this field afive (integer).Then multiply it by the cell area.

Now just calculate the count of cells with all other values in the polygon and store this in the polygon This is merely the count value in ArcGIS for an integer raster. Call this filed aother. (integer) Then multiply it by the cell area.

Create a new filed field called answer (double precision)

Then in the field calculator answer = afive/aother

You can achieve this in raster by clipping the raster to the polygon extent (extract by mask) the multiplying the counts by the values.

Some help

http://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/raster-dataset-attribute-tables.htm http://desktop.arcgis.com/en/arcmap/10.3/manage-data/tables/making-field-calculations-making-simple-field-calc.htm

Improve this answer
2
  • Thanks a lot! Do I need a projection before doing this?
    – D_B
    Commented Feb 25, 2019 at 19:50
  • no you likely do not
    – If you do not know- just GIS
    Commented Feb 25, 2019 at 22:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.