Help! Kriging or IDW tools for soil mapping

[LindsayMyron]

Hi!

I'm working on a soils map, the data for which I've collected with a EM38 (electrical conductivity) instrument.  The resulting attribute table is quite large, but there is a single column, "X5", with the data (in milliSiemens) that I'm wanting to map.  The area has 1000+ data points over 30 acres and I'd like to use either the kriging or IDW tools to interpolate the points into a even map. 

My issue so far is that when I open up the kriging or IDW tools' window and select the layer with the EM data, the next drop down menu (I believe it's called the Z value?) does not include the X5 column; the drop down only lists columns such as latitude, longitude, date, time, etc.  How can I add the X5 column to that drop down menu? Is this because of the type of field?  I believe the X5 column is in String format.

Pardon my incorrect use of language, I don't have the window in front of me.  But I hope you understand what I'm talking about!

Any suggestions would be much appreciated!!

Cheers,

Lindsay

[DanPatterson_Retired · Accepted solution]

you have to ensure that the data to be mapped is numeric...just because it has a number in the column doesn't mean it is numeric...you have to check the field properties to assess this.  For example, a shapefile's table will show numeric data right-justified whereas text/string data will be left justified.  You can convert these data to numeric by adding a new column to the table, use the field calculator  and the python interpretor with the expression

float(!your column name here!)

This assumes that all of the data in the column can be converted to a number...if it doesn't, then there a few extra hoops you have to go through

[LindsayMyron]

Great!  Problem solved.  Thanks so much!

[LindsayMyron]

Okay, so I now I think I have a new problem.  I was able to use the Kriging tool, with success, after I converted the data column to a numerical format (I changed it to "float").  However, whenever the tool is finished the data in the column has been changed. 

The original column of data had a range between ~0-100, but after kriging, the data has been reduced to within a range of 0-10.  In other words, data points that were above 10 had the decimal point shifted over (e.g. 58.9 became 5.89, 13.5 became 1.35). 

Any idea why this is happening?

[DanPatterson_Retired]

The initial thread isn't closed.  You should start a new question since the problem is different