It should also be noted that the Vault 101 map marker is not counted in the Pip-Boy 3000 'discovered locations' statistic, resulting in a maximum displayed value of 162 discovered locations (161 without Lawbringer).
Without any of the available add-ons installed, there are 163 marked locations in Fallout 3 provided you have the Lawbringer perk without it there are only 162 as the Regulator HQ is not available.
