This section is accesible through Plugins section by selecting the Masking tab.
Here you can install/uninstall and disable/enable this plugin as any other.
Upon installation, this plugin will create a mask layer that will limit the visible area of the map for users with a role that extends masking role.
By default only administrators have access to this layer.
To create an allowed zone for a role - just enable editing for the Masking layer in map section and add a polygon.
In the Manage attributes section specify a role in role_view field (this will make all users who extend this role visualize data only inside this polygon),
and a role in role_edit field (this will make all users who extend this role edit data only inside this polygon).
Note: If you create N different zones and assing them to the same role - users that extend this role will be able to view or edit data only in this N zones.
Note: Only roles that extend the masking role will be available in the manage attributes section.