Patches are a special kind of stationary agents in NetLogo that make up the world of a model. You can think of the patches as the squares that make up a chessboard.

The patch primitive reports the specific patch with the given coordinates. For example, if we wanted to create a model of an ant colony whose entrance was the patch at the center, we could write the following code:

ask patch 0 0 [
    set pcolor green

The patches primitive reports all the patches in the model. This primitive is helpful in asking all the patches to do the same things (e.g., change pcolor) or narrow down a subset of patches. For example, if we wanted to create a forest fire model with some green patches representing trees, some green patches representing ground, and the leftmost patches representing the fire (red), we would write the following code:

ask patches [
    set pcolor one-of [green brown]
ask patches with [pxcor = min-pxcor][
    set pcolor red

Things to keep in mind when using patch and patches:

In the model example below, we have a farm that is surrounded with a fence. The fence is represented with brown patches and the grassland is represented with green or lime patches. We also have a yellow square in the middle that represents a ranch and some cows who move around randomly and eat the grass on each patch until there is no grass left.


Try it Yourself