Wireless Area

Area is a part of a mesh network, for limiting station access to a certain number of APs (e.g., a building or a block). All APs within the mesh may have the same SSID, but stations will select only a few ones, based on their area code.

The Area setting is configured on APs in the wireless menu. This can be done with the goal to limit connectivity (to force the station to stay within a certain area) , or to improve connection quality (as the station will not try to connect to APs from other areas, which may have worse signal quality).
[admin@router] /interface wireless> set wlan1 area=

The stations can be configured to connect to any AP that has its area code beginning with a certain string (area-prefix parameter in wireless connect list), so you configure areas within areas, and make some stations only work within a subarea, and allow some other stations to work within a larger area.
[admin@router] /interface wireless connect list> add area-prefix=

For example stations with area-prefix="area1" will connect to any AP with area code "area1.1" and "area1.2", but if you specify area prefix as "area1.1", then that station will only connect to APs with area code "area1.1"; you can subdivide areas even further.