How to analyse data

[Kofi_Lartey]

I am trying to do some form of correlation analysis between elevation and rainfall erosivity, but not sure whether this is the right way. I used the fishnet tool to evenly distribute a set of points over a polygon. Next i used the extract multiple values to point tool in spatial analyst - extraction to combine a DEM and the shapefile of points to extract from the DEM points with elevation and coordinates. Now the output will be joined to the rainfall erosivity map from which some form of correlation analysis can be performed, i believe. However there is a problem. The output from the multiple point extraction was two empty columns, one from the DEM and the other from the shape file. I believe i am not doing something right. I welcome

suggestions to give me direction. Attached is the shape file

[ChrisDonohue__GISP]

Let me add an expert on thisDan Patterson

Chris Donohue, GISP

[Kofi_Lartey]

Dan Patterson​, I hope you will have time to comment on my latest post on some form of correlation analysis between rainfall erosivity and  elevation

[DanPatterson_Retired]

There are a variety of tools in the Spatial Statistics toolset Spatial Statistics toolbox sample applications—Help | ArcGIS for Desktop

If you are looking to do this in a spatial context but your data are interpolated values, so I would advise against it..

Since you are extracting values from surfaces not using observation points, but from a grid, correlation and regression wouldn't be advisable.  You might want to look at looking for 'associations' beween the two variables.  I would suggest reclassifying the two layers to and using the combine tool Combine—Help | ArcGIS for Desktop to denote the associations that may arise between elevation and  erosivity.

However... it is not elevation per se that will contribute to erosivity directly, but through its terrain derivatives such as slope (steep slopes--> high erosive potential) and even aspect (dominant direction to prevaling weather perhaps). 

There is also the cavaet, that elevation or its derivatives (slope etc) can't be used in determining a correlation with a variable that may be derived from it.  So if the determination of erosivity index/value requires elevation, then you shouldn't be correlating the two since a tenant of correlation is independence of the variables

[Kofi_Lartey]

@Dan I am looking at various options and then i will decide which could be useful, but that comment was very useful