Why do area calculations return negative values?

[BARBARANJIRU]

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

[KishorGhatage · Accepted solution]

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.

[JayantaPoddar]

Hi Barbara,

It could be a geometry issue.

Try Repair Geometry (Data Management Tools)

Thanks,

Jay

[XanderBakker]

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...

[BARBARANJIRU]

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

[XanderBakker]

Hi BARBARA NJIRU‌

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

Kind regards, Xander

[KarinHagan]

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

[ScottMoyer]

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

[KarinHagan]

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