topic Calculate Areas giving negative values in Spatial Statistics Questions

Calculate Areas giving negative values

MarceloLago — Fri, 25 Oct 2013 17:11:54 GMT

Hi,

The calculation of areas on the attached polygon shape file gives negative values. I am using ArcMap 10 service pack 5.

Is this a bug?

Thanks, Marcelo.

Re: Calculate Areas giving negative values

CarolaEklund1 — Fri, 25 Oct 2013 17:25:37 GMT

Hi Marcelo,

one of our users had the same problem a while ago. If I remember right, one cause could be that the polygons were digitzed in a counter clockwise direction; it's also possible that the polygon features are (self) intersecting. (or a combinationof both?)
I think to fix this you will have to run the "Repair Geometry" tool (ArcToolbox -->Data Management Tools -->Features -->Repair Geometry). Select your polygon shp file/feature class as "Input Features". (in our case we also unchecked "Delete Features with Null Geometry")
Hope that helps!

Carola

Re: Calculate Areas giving negative values

MarceloLago — Fri, 25 Oct 2013 17:41:56 GMT

Thank you Carola, repairing the geometry worked fine.

The absolute values of the calculated area were accurate. ArcMap just assigned negative values when "incorrect ring ordering". I guess this would be an easy fix for the developers. 🙂

Thank you again, Marcelo.