Sampling land cover map using ArcGIS Desktop?

Question

I have a little bit of a sampling problem in ArcGIS Desktop. I have a classified map with 7 Landcover classes, and this classes are as follows with their percentage: Forest=20.9%, agriculture=6.3%, grassland=67.8%,water=1.50%, wetland=3.4% etc. I am generating 10000 random points and I want to distribute it according to the % or area of each class to total class (990615ha). e.g for forest 20.9/100*990615= 10000, agriculture 5.9/100*10000=622, grassland 67/100*10000=6651,

How do I generate the sample points assigning specific samples to each class ?

If I generate random points with the landcover map, it assigns randomly and disproportional to the class area and total area.

I have an X tool, I read it is possible with x tools but I cannot figure it out.

Answer 1

If you want a sample of 10000 point with the same proportion as in your land cover map, you should use a simple random sampling. In fact, the simple random sampling will not give you exactly the same proportions, but it will give you exactly the same proportions ON AVERAGE. Still, this is statistically better to work like this, and most of the time you will end up close to these proportions (especially with 10000 points).

In practice, you need to use "create random point", located in Data mamangement > sampling. Then you can extract the values at each point location using "spatial analyst > extraction > multivalue to point".

If you really want a precise number of points, you should convert your raster to polygon, dissolve based on the number of classes, then add a field with the required number of points per feature. Then with the same "create random point" as above, use the "field" option to tell how many points you want for each land cover type.