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 | 11 | -3 | -4 | -1 | 2 | 0 |
| LAB | 22 | 16 | -6 | -6 | -1 | 1 | 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 | 29 | -11 | -11 | -3 | 3 | 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: Aberavon; Aberconwy; Arfon; Cardiff Central; Carmarthen West and Pembrokeshire South; Delyn; Gower; Islwyn; Montgomeryshire; Newport East; Pontypridd.
The old seats which are lost to another party are: Alyn and Deeside; Carmarthen East and Dinefwr; Ynys Mon.
The new seats which are gained from another party are: Alyn and Deeside; Carmarthen; Anglesey and Bangor.
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Alyn and Deeside | 100% of Alyn and Deeside | 31.5% of Delyn |
| Clwyd South and North Montgomeryshire | 56.2% of Clwyd South | 43.5% of Montgomeryshire
21.4% of Clwyd West
16.4% of Vale of Clwyd
|
| Conwy and Colwyn | 72.0% of Clwyd West | 67.1% of Aberconwy
12.6% of Vale of Clwyd
|
| Rhuddlan and Flint | 71.0% of Vale of Clwyd | 68.5% of Delyn |
| Wrexham | 100% of Wrexham | 43.8% of Clwyd South |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Carmarthen | 92.4% of Carmarthen East and Dinefwr | 40.8% of Carmarthen West and Pembrokeshire South |
| Ceredigion and North Pembrokeshire | 100% of Ceredigion | 23.8% of Preseli Pembrokeshire
7.6% of Carmarthen East and Dinefwr
8.4% of Montgomeryshire
|
| Llanelli | 100% of Llanelli | 32.0% of Gower |
| Pembrokeshire Mid and South | 76.2% of Preseli Pembrokeshire | 59.2% of Carmarthen West and Pembrokeshire South |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Blaenau Gwent | 100% of Blaenau Gwent | 48.8% of Islwyn |
| Caerphilly | 63.9% of Caerphilly | 46.5% of Islwyn
20.7% of Newport West
|
| Monmouthshire | 87.9% of Monmouth | 35.9% of Newport East |
| Newport | 68.9% of Newport West | 64.1% of Newport East |
| Torfaen | 100% of Torfaen | 12.1% of Monmouth
10.3% of Newport West
|
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Anglesey and Bangor | 100% of Ynys Mon | 42.5% of Arfon
13.8% of Aberconwy
|
| Gwynedd | 100% of Dwyfor Meirionnydd | 57.5% of Arfon
19.2% of Aberconwy
6.6% of Clwyd West
|
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Bridgend and Vale of Glamorgan West | 100% of Bridgend | 20.2% of Vale of Glamorgan
2.0% of Ogmore
|
| Cynon Valley and Pontypridd | 100% of Cynon Valley | 50.0% of Pontypridd |
| Merthyr Tydfil and Rhymney | 100% of Merthyr Tydfil and Rhymney | 36.1% of Caerphilly
4.7% of Islwyn
|
| Ogmore and Aberavon | 91.3% of Ogmore | 58.8% of Aberavon |
| Rhondda and Llantrisant | 100% of Rhondda | 45.2% of Pontypridd
6.7% of Ogmore
|
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Brecon, Radnor and Montgomery | 100% of Brecon and Radnorshire | 48.2% of Montgomeryshire |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Cardiff North | 93.6% of Cardiff North | 37.6% of Cardiff Central
0.2% of Cardiff South and Penarth
|
| Cardiff South and East | 54.2% of Cardiff South and Penarth | 62.4% of Cardiff Central
6.4% of Cardiff North
|
| Cardiff West | 100% of Cardiff West | 16.1% of Cardiff South and Penarth
4.8% of Pontypridd
|
| Vale of Glamorgan East | 79.8% of Vale of Glamorgan | 29.5% of Cardiff South and Penarth |
| New seat | Primary component | Secondary component(s) |
|---|---|---|
| Gower and Swansea West | 82.9% of Swansea West | 46.0% of Gower
10.6% of Swansea East
|
| Neath | 100% of Neath | 41.2% of Aberavon |
| Swansea East | 89.4% of Swansea East | 22.0% of Gower
17.1% of Swansea West
|