Negative values after areal interpolation

[ShuoLiu]

Hi, guys.
I have a problems using Areal Interpolation in ArcGIS 10.1.
There's no negative value in my origin data.
And there's no negative in my predicted surface.
But after I used Areal Interpolation layer to to Polygons,there are 75 polygons with a negative value, which they really shouldn't be.
Any ideas why this happened?

[EricKrause]

Areal Interpolation will often predict outside of the data range.  This means that sometimes you can get negative predictions for a phenomenon that can't be negative.  Unfortunately, there isn't much you can do to prevent this.

Does your data represent counts?  If it does, you should use Event (overdispersed Poisson) areal interpolation.  This type of areal interpolation will never predict negative values.

[JoshObrecht]

What if we don't have count data? Is there a way to not get negative numbers?

[EricKrause]

We have special models for count and proportion data, but if your data is a continuous variable (like average temperature or median age), you may end up with negative predictions.

You may be able to change the semivariogram parameters to get only positive predictions, but it's difficult to say exactly what you should change because everything is so data-dependent.

[ttgrdias]

Hi!

@EricKrauseis there any way to avoid negative prediction values using EBK3D?

Tks,

[EricKrause]

@ttgrdias If all of the input data values are positive (no negatives or zeros), then the Log Empirical transformation ensures all predictions will be positive.

[ttgrdias]

@EricKrause Ok, thanks. But that doesn't allow to introduce measurement errors, correct?