By the way, if you are wondering what the C1 codes are for - this is how they are actually referred to in the Local Government Act 1972.
It creates counties in England and Wales, and districts in the metropolitan counties, and all the Welsh counties. But it doesn't actually name any of the districts! These were specified by an order made by the Secretary of State later on.
Additionally, all the non-metropolitan districts were created in another order later on. I don't have the reference for this, and fear it isn't in print, anyway.
- C1 - Colwyn - Colwyn Bay
- C2 - Rhuddlan - Rhuddlan town
- C3 - Delyn - ?
- C4 - Alyn and Deeside - River Dee - River Alyn
- C5 - Glyndwr - Owen Glendower
- C6 - Wrexham Maelor - Wrexham, and Maelor
- D1 - Ceredigion - ancient name (from 5th c Ceredig)
- D2 - Preseli - Preseli hills
- D3 - South Pembroke - southern part of Pembrokeshire
- D4 - Carmarthen - town
- D5 - Llanelli - Llanelli town
- D6 - Dinefwr - castle and estate near Llandeilo (estate 18th c, castle on the estate perh 13th?)
- GT1 - Newport - town
- GT2 - Islwyn - Mynyddislwyn (mountain) in Gwent, grid ref ST195945, name also taken as bardic name by Welsh poet long before the constitency, and as Roy Hughes when he became a Lord.
- GT3 - Blaenau Gwent Erm, "heads/ends of the valleys of Gwent"? Ish? :) The A465 road along the heads of the valleys is ffordd y blaenau in Welsh.
- GD1 - Anglesey - island
- GD2 - Dwyfor - River Dwyfor
- GD3 - Arfon - historic name
- GD4 - Aberconwy - village called Aberconwy, River Conwy
- GD5 - Meirionnydd - historic name
- MG1 - Ogwr - valley of the river Ogmore (Welsh Afon Ogwr)
- MG2 - Rhondda - valley of the river Rhondda
- MG3 - Cynon Valley - valley of the River Cynon
- MG4 - Merthyr Valley - valley of the river... erm, Taff :) No. Valley with Merthyr Tydfil in it (also a mountain, Mynydd Merthyr, overlooking it). Merthyr is the Welsh for martyr (Tydfil was the martyr).
- MG5 - Rhymney Valley - valley of Rhymney River
- MG6 - Taff-Ely - valley of (lower) River Taff and river Elai
- P1 - Montgomery - old county name
- P2 - Radnor - old county name
- P3 - Brecon - old county name
- SG1 - Cardiff - city
- SG2 - Vale of Glamorgan - area name
- WG1 - Swansea - city
- WG2 - Lliw Valley - river Lliw (flows parallel to Tawe then into Llwchwr; there's two Lliw reservoirs)
- WG3 - Neath - town (in turn named after river Neath)
- WG4 - Port Talbot - town (Talbots not a river! -- a cadet branch of Shrewsburys, apparently)