Each new seat can be described as a combination of parts of old seats. These tables show this decomposition. The winner of the old seat at the 2019 election is shown by party colour, as is the implied winner of the new seat.
The implied results are calculated using the local election results for the wards which make up each old seat. This should give the most accurate projection, since it reflects varying political behaviour across the seat.
| Party | Old Seats | New Seats | Change | Disappear | Switch Out | Switch In | Fresh |
|---|---|---|---|---|---|---|---|
| CON | 14 | 12 | -2 | -3 | 0 | 1 | 0 |
| LAB | 22 | 18 | -4 | -4 | 0 | 0 | 0 |
| LIB | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Brexit | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Green | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Plaid | 4 | 2 | -2 | -1 | -1 | 0 | 0 |
| MIN | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Total | 40 | 32 | -8 | -8 | -1 | 1 | 0 |
The table shows how the various changes affect each party in this area. The total old and new seats are shown for each party, as well as their difference ('Change'). The change in seats is also explained through the four explanations:
The old seats which are disappearing are: Arfon; Carmarthen West and Pembrokeshire South; Clwyd South; Cynon Valley; Newport West; Ogmore; Swansea East; Vale of Clwyd.
The old seats which are lost to another party are: Carmarthen East and Dinefwr.
The new seats which are gained from another party are: Caerfyrddin (Carmarthen).
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Alyn and Deeside | 100% of Alyn and Deeside | 23.1% of Delyn |
| Bangor Aberconwy | 100% of Aberconwy | 40.9% of Arfon
14.2% of Clwyd West
|
| Clwyd East | 76.9% of Delyn | 35.9% of Vale of Clwyd
16.1% of Clwyd West
9.1% of Clwyd South
|
| Clwyd North | 69.8% of Clwyd West | 64.1% of Vale of Clwyd |
| Wrexham | 100% of Wrexham | 39.2% of Clwyd South |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Caerfyrddin (Carmarthen) | 84.2% of Carmarthen East and Dinefwr | 40.7% of Carmarthen West and Pembrokeshire South |
| Ceredigion Preseli | 100% of Ceredigion | 30.1% of Preseli Pembrokeshire |
| Llanelli | 100% of Llanelli | 15.8% of Carmarthen East and Dinefwr |
| Pembrokeshire Mid and South | 69.9% of Preseli Pembrokeshire | 59.3% of Carmarthen West and Pembrokeshire South |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Blaenau Gwent and Rhymney | 100% of Blaenau Gwent | 20.3% of Merthyr Tydfil and Rhymney
9.2% of Caerphilly
4.8% of Islwyn
|
| Caerphilly | 90.8% of Caerphilly | 24.6% of Islwyn |
| Monmouthshire | 88.2% of Monmouth | 23.0% of Newport East |
| Newport East | 77.0% of Newport East | 45.8% of Newport West |
| Newport West and Islwyn | 70.6% of Islwyn | 54.2% of Newport West |
| Torfaen | 100% of Torfaen | 11.8% of Monmouth |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Dwyfor Meirionnydd | 100% of Dwyfor Meirionnydd | 59.1% of Arfon
5.1% of Clwyd South
|
| Ynys Mon (Anglesey) | 100% of Ynys Mon |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Bridgend | 82.8% of Bridgend | 31.8% of Ogmore |
| Merthyr Tydfil and Aberdare | 79.7% of Merthyr Tydfil and Rhymney | 58.1% of Cynon Valley
0.0% of Brecon and Radnorshire
|
| Pontypridd | 70.9% of Pontypridd | 41.9% of Cynon Valley
16.4% of Ogmore
|
| Rhondda and Ogmore | 100% of Rhondda | 24.2% of Ogmore
15.4% of Pontypridd
|
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Brecon, Radnor and Cwm Tawe | 100% of Brecon and Radnorshire | 30.4% of Neath |
| Montgomeryshire and Glyndwr | 100% of Montgomeryshire | 46.6% of Clwyd South |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Cardiff East | 78.2% of Cardiff Central | 32.4% of Cardiff South and Penarth |
| Cardiff North | 100% of Cardiff North | 4.7% of Pontypridd
0.1% of Cardiff South and Penarth
|
| Cardiff South and Penarth | 67.5% of Cardiff South and Penarth | 21.8% of Cardiff Central
8.3% of Vale of Glamorgan
|
| Cardiff West | 100% of Cardiff West | 8.9% of Pontypridd
1.2% of Ogmore
|
| Vale of Glamorgan | 91.7% of Vale of Glamorgan |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Aberafan Maesteg | 83.8% of Aberavon | 26.4% of Ogmore
17.2% of Bridgend
1.6% of Neath
|
| Gower | 90.8% of Gower | 33.9% of Swansea West
1.0% of Swansea East
|
| Neath and Swansea East | 68.0% of Neath | 37.4% of Swansea East
16.2% of Aberavon
9.2% of Gower
|
| Swansea West | 66.1% of Swansea West | 61.6% of Swansea East |