2

Fairly new to ArcMap 10.3, I'm trying to find a method to build a toolbox model to determine the area of flooding within a basin. The tricky part is that I need to remove the flooding within a pond.
Visually, the pink box is the basin, the light pink polygon is the pond, and the green is the flooding area.  What I am trying to calculate is the area of green that is on the white background over the total area of white.

Visually, the pink box is the basin, the light pink polygon is the pond, and the green is the flooding area. What I am trying to calculate is the area of green that is on the white background over the total area of white.

Using the toolbox I currently have "Intersect" (to cut the flooding polygons within the basin so its not double counted), then "Union" (to determine flooding within the ponds), then "Select" (which removes the flooding within the pond).
From here I was just going to use a "Calculate Field" Tool since each step has determined the area of the new polygon. Except every time I run the same files it provides a different answer or changes the name which means I have to change my calculate field tool.

I'm trying to automate the process since I need to move onto another project and this needs to be done for twelve flooding events every year.

I've tried using "Add Geometry Attributes" But it always seems to break the model string and keeps giving me the following error "ERROR 000229: The data is not accessible. It is likely either invalid or not available." I usually add this action after "Select" then "Spatial Join" to be able to add a extra fields before "Calculate Field". Sometimes the add geometry works but 90% of the time it doesn't.

I only have access to basic ArcMap which means many of the answers provided for finding area that are similar I don't have access to, (ex, "Difference", or "Raster")

1

It is critical that your map/datalayers are in a projected coordinate system when calculating area or distances. If the same projection is used consistently, you should get consistent answers when calculating geometry.

If you are going to discard the area that is flooded within the pond, you can use the Erase tool instead of the Union. Erase needs an Advanced level license but equivalent functionality can be obtained using Union followed by Select.

  • The projection as been set and all of the shapefiles are within a geodatabase with the same projection determined. My understanding was that the geodatabase would confirm that the project coordinate system would remain the same for all of the shapefiles within. – Elizabeth Aug 16 at 21:28
  • 1
    A geodatabase does not necessarily guarantee all feature classes are in the same projection. A geodatabase can store feature classes with different projections, the exception is if you create a feature dataset within a geodatabase. All features within a feature dataset must have the same projection. There is no way you can get significantly different results if you are using a consistent projection. Just to clarify, you are using a projected coordinate system, not a geographic coordinate system, correct? – RGfromRWBJV Aug 16 at 21:35
0

You shouldn't need to use "Add Geometry Attributes" but just need to add a numeric field and calculate the value with "Calculate Geometry" directly in the table. For the 000229 error you might want to try to disable background geoprocessing as suggested in this ESRI technical article 000012177.

It sounds like (from your description) that you have some overlap between the flooding and the pond so I think I'd just put all three layers (assuming they are separate layers) into the same intersect operation.

I would approach this by adding a new numeric (double) field to use for calculating the geometry in the basin and calculate it as a first step before doing the intersection (to use as the original area). Then I'd perform the intersection to know the area of the basin affected by flooding that is not part of the pond. I think that the intersect is the only output you'd need. With the original area calculation done at the beginning you have the full basin area to use for calculating percentages or whatever you would need.

screenshot of calculate geometry in the table

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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