select polygons that contain more than 50% of intersecting layer

Question

I would like to select out areas that are both permitted (PermitAreas.shp) AND contain more than 50% irrigation (IrrigatedLands.shp).  If you just wanted ???irrigated??? it would be fairly easy but I cannot figure out a way to select areas that contain more than 50% irrigation. 50% is an arbitrary number???.we may want 20, 30 etc.

I am not sure if I should do a combination of unions, intersections etc. Or if I would be better of building a model and use some kind of python script? I have little experience with model building or python scripting. I can do this in 9.3 or 10. Thanks!

BethHoobler · Answer

Thank you so much! It worked perfectly and we got the exact results that we wanted. I did a lot of unions and intersects but never the right combination. I truly appreciate your taking the time to respond!

Beth

DonovanCameron · Answer

First, I would select the permit areas that are being intersected by an irrigation area and vice versa.
This can be done with a Select by Location from the Selection tab.

Then export those selections to a new feature class/shapefile.

Take the new Permit selection feature class and generate the area in the attribute table by creating a new integer field (called [Permit_Area] or something) and running a Calculate Geometry.

Two options here...
Run a union with both the irrigation selection and permit area selection as the inputs. This will allow you to query out the areas from the irrigation that overlap the permit area and create a new feature class with that selection.

or

Run an Intersect tool to extract the overlapping irrigation areas immediately. I would recommend using this method as the attributes from the [Permit_Area] can be carried over to the newly created intersection feature class showing only the areas of the irrigation area that overlap the permit area.

Now take this intersected feature and create a new integer field called [Overlap_Area] and Calculate Geometry to get the results.

You will now have a feature class with two area fields, one that shows the area of the entire permit area that would intersect that irrigation area and the other showing the area of just the overlapping portion of the irrigation area.

Create a new integer (float, Precision:6 Scale:3) field to get the percentage now. Use the field calculator with this expression:[Overlap_Area] \ [Permit_Area] * 100

and that should result in your percentage.

BethHoobler · Answer

The first one...where 50% of the permit area is taken up by irrigation. Can you  help?