clear-patches is a primitive that resets all the patches at once. It makes the values of the custom patch variables (defined with the patches-own primitive) to their default initial values and makes all the patches black. You can also use its shorthand version cp in your code.

clear-patches is only used when we do not want to use clear-all. For example, if we wanted to clear the patches but keep some global variables’ values and the existing turtles the same, we would use clear-patches.

In the model example below, we have three buttons. The first one makes the patches' color green and creates some cows on random locations. The second button runs the clear-patches primitive to clear the patches, as a proxy for grass, but leaves the cows the same. The third button runs the clear-turtles primitive to remove the cows from the model but leave the patches/grass as is.