Anyone can join a Publicly Visible Tree Map. By default new users are set to the public User Role. If you don't want these users seeing certain information or making edits, be sure to update the permissions for the public User Role.
If your Tree Map is not Publicly Visible, only users that you have invited will be able to view or join your Tree Map. Anyone who tries to access your Tree Map will be asked to log in first. By default new users are set to the public User Role, so be sure to update the public permissions or assign users to a new User Role if you want them to have additional access. A user will be added to your map's list of users once they edit one or more fields on your map. If they simply view with map as a public user, they will not be added to your list of users unless you invited them to join them map.
By default Maps are not Publicly Visible. To change this setting, select "Manage" from the navigation bar at the top and then click on "General" in the Administration menu on the left. Choose "Basic Information". Click "Edit" in the top right. Check the Public Visible box to make your map visible. Uncheck the Publicly Visible box to hide your map.