# some kriging issues

Discussion created by do123456 on Nov 4, 2011
Latest reply on Nov 7, 2011 by EKrause-esristaff
Hello all,

I'm currently using the Geostatistical Analyst to perform some kriging interpolations, and interpret the results. However, I unfortunately stumbled up some questions, which I hope you have the answers for:
First of all, when assigning weighting values to the points, I noticed that some points are assigned negative values. I understand how they come there (inverse of a matrix), but: what does that mean. How can points account negatively to an unknown point?

Second question gets more clear in the example: I have a point file of monitoring wells measuring phreatic groundwater levels. I want to say something about the maximum distance between these wells in order to have a maximum uncertainty in an area (for instance a village, where houses can be damaged due to high or low water tables). So I set a level: I don't want my standard error to be larger than 20 centimeters, a value that does occur on the prediction error map. I thought that I should take the square of 20 cm, 4cm^2 as semivariance input to the model and that the x-value was then my maximum distance of the wells (which could be easily turned into a preferred well density). However, in the table of the exported semivariogram, this value of 0.04 doesn't exist, in fact, only the non-squared values of the map are in that table. So I wonder: how can it be that the values of the semivariance - which is given in [m^2] - are the same as the values of the prediction error map - given in [m].

I hope you can help me with it.

Best regards, and thank you in advance,

Erik (Dirk's trainee)