topic Re: Why do area calculations return negative values? in Geoprocessing Questions

Why do area calculations return negative values?

BARBARANJIRU — Mon, 02 Feb 2015 12:59:01 GMT

hello,

i am trying to calculate area of several polygons using calculate geometry and i am getting the area with negative values. the projected coordinate system is Arc 1960 UTM zone 37S. i cant figure where the problem is. kindly help

Re: Why do area calculations return negative values?

KishorGhatage — Mon, 02 Feb 2015 13:23:41 GMT

1. Take a backup of your data.

2. Run Check geometry.

3. Run repair geometry.

4. Then try calculating area in a new field with double data type.

Re: Why do area calculations return negative values?

JayantaPoddar — Mon, 02 Feb 2015 13:27:44 GMT

Hi Barbara,

It could be a geometry issue.

Try Repair Geometry (Data Management Tools)

Thanks,

Jay

Re: Why do area calculations return negative values?

XanderBakker — Mon, 02 Feb 2015 13:31:01 GMT

This is caused by incorrect orientation of the polygons rings. As Kishor Ghatage‌ suggests, repairing the geometry will probably solve the problem. If you work with a featureclass in a file geodatabase, you do not need to recalculate the area, this will be done automatically...

Re: Why do area calculations return negative values?

BARBARANJIRU — Tue, 03 Feb 2015 07:35:59 GMT

Thank you. did run repair geometry and it worked perfectly..

Re: Why do area calculations return negative values?

XanderBakker — Tue, 03 Feb 2015 11:35:45 GMT

Hi BARBARA NJIRU‌

Could you mark the answer by Kishor Ghatage‌ as the correct one? Thank you.

Kind regards, Xander

Re: Why do area calculations return negative values?

KarinHagan — Wed, 25 Mar 2015 14:30:27 GMT

FYI, this happens when your polygon is drawn "backwards". Polygons should be drawn clockwise. If drawn counter-clockwise, you'll have negative areas. There's a similar phenomenon with polylines.

And THANK YOU to Kishor for the solution! I have a dataset created by a modeling software in which half of the polygons (17,000) were drawn backwards. Due to the negative geometry, I couldn't work with the dataset at all.

Karin

Re: Why do area calculations return negative values?

ScottMoyer — Thu, 26 Mar 2015 16:50:57 GMT

Karin,

As ArcGIS cannot create invalid geometries (Why do area calculations return negative values?) are your "backwards" polygons being created in another program and being brought into ArcGIS?

Scott

Re: Why do area calculations return negative values?

KarinHagan — Thu, 26 Mar 2015 17:07:24 GMT

Hi Scott,

You can actually do it if you draw your polygon counterclockwise. In the particular case I was working on yesterday, yes, the polygons came from an external modeling software.

Karin