Ordnance Survey has a helpline on 08456 05 05 05 and customerservices@ordnancesurvey.co.uk who will be able to advise on how to do this.
Mae llinell gymorth gan yr Arolwg Ordnans ar 08456 05 05 05 a customerservices@ordnancesurvey.co.uk a fydd yn gallu rhoi cyngor ar sut i wneud hyn.