Llandaff is located about two miles north-west of Cardiff City centre and is on an area of rising ground beside the River Taff.  The elongated hill on which it stands is the remains of a rock outcrop which, in prehistoric times, would have been the nearest piece of dry land to the sea.  The surrounding flat land, such as Llandaff Fields, would have been swampy marshland, difficult to cross and liable to flooding.  

The Cathedral is sited below the rest of the village on a narrow shelf between the base of the hill and the River Taff.  This position was probably chosen because it was near the old river crossing and was also partly hidden from intruders.  The site would also have been well served by a line of wells and natural springs along the scarp of the hill.