Why do area calculations return negative values?

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02-02-2015 04:59 AM
BARBARANJIRU
New Contributor

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

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Accepted Solutions
KishorGhatage
Occasional Contributor III

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.

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8 Replies
KishorGhatage
Occasional Contributor III

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
MVP Esteemed Contributor

Hi Barbara,

It could be a geometry issue.

Try Repair Geometry (Data Management Tools)

Thanks,

Jay



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XanderBakker
Esri Esteemed Contributor

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
New Contributor

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

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XanderBakker
Esri Esteemed Contributor

Hi BARBARA NJIRU

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

Kind regards, Xander

KarinHagan
New Contributor

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

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ScottMoyer
Occasional Contributor

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

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KarinHagan
New Contributor

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

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