Dear list,

I have a Landcover classification Shapefile (shp) with 3 classes and I want to validate it by stratified random based on the total area of each class and a total number of sample points (~600).

Class1     6.6%  resulting points ~ 50 
Class2  62.3% resulting points   ~ 375
Class3  31.1%resulting points ~  190

I gave a look at the spsample
spsample(shp, n=600, type='stratified') 
but what I'm missing here is the class information for distributing points.

Thanks for help, Matteo
    


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