neighbors4 reports an agentset that contains the four patches that surround an agent's current patch in the north, east, west, and south directions. Both turtles and patches are allowed to use this reporter. For example, if we wanted to create a model in which a fire spread from one patch to its neighbors, we would write the following code:

ask patches [
    if pcolor = red [
        ask neighbors4 [
            if pcolor = green [
                set pcolor red
            ]
        ]
    ]
]

Things to keep in mind when using neighbors4:

• neighbors4 will always report patches even if we use it within an ask turtles context. If you would like an agent to see neighboring turtles, you can use turtles-on neighbors4.
• There is also a neighbors primitive that reports all eight neighboring patches.
• Be mindful of world-wrapping when using neighbors4 as a patch at the edge of the world will report the patch on the other end of the model as its neighbor. If you turn off world-wrapping, then a patch will report either two patches if it is on the corner or three patches if it is at the edge.

In the model example below, there is a fire spreading in a forest. A patch on fire will spread to its neighboring patches in cardinal directions that contain trees. If a fire patch has brown neighboring patches that indicate ground, it will turn the ground patches gray to indicate the edge of the forest fire.