Mapping Mountains – Significant Height Revisions – 600m Twmpau and The Welsh Highlands – Uchafion Cymru

Craig Ysgafn (SH 659 443) 

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and the The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

LIDAR image of Craig Ysgafn (SH 659 443)

The criteria for the two listings that this height revision applies to are:

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format.

600m Twmpau by Myrddyn Phillips

The Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

The Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Craig Ysgafn and it is adjoined to the Moelwyn Mawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the A4085 road to its west, the A487 road to its south and the A496 road to its east, and has the town of Blaenau Ffestiniog towards the east north-east.

When the list of Welsh 500m P15s that later became known as the The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 26m of drop, based on the 689m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 663m bwlch height, based on interpolation of 10m contouring between 660m – 670m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Craig Ysgafn (SH 659 443)

LIDAR analysis gives the summit of this hill as 690.0m positioned at SH 65994 44332, and when compared to its originally listed summit height this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 690.0m and this was derived from LIDAR analysis, this is 1.0m higher than the originally listed summit height of 689m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and importantly this height signifies that an uppermost 690m ring contour is missing from this map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moelwyn Mawr

Name:  Craig Ysgafn

OS 1:50,000 map:  124

Summit Height (New Height):  690.0m (LIDAR)

Summit Grid Reference:  SH 65994 44332 (LIDAR)  

Bwlch Height:  663.4m (LIDAR)

Bwlch Grid Reference:  SH 66001 44596 (LIDAR)

Drop:  26.6m (LIDAR)

 

Myrddyn Phillips and Aled Williams (May 2026) 

Monthly Synopsis

 

Synopsis of all major changes detailed on Mapping Mountains during the last calendar month.  These can include new, confirmation and retrospective changes

 

Hill Reclassifications: 

Carreg Rhoson (SM 664 253) - 30-99m Double Sub-Twmpau addition

Rhos Swydd (SO 117 650) - 200m Sub-Twmpau addition

Pen y Garfan (SN 727 512) - 400m Sub-Pedwar addition

Rhos Goch (SO 182 859) - Sub-Four addition

 

Significant Height Revisions: 

Troed Rhiw Bylchau (SN 761 471) - Y Trichant - The 300m Hills of Wales

Mason's Bank (SO 228 873) - The Fours - The 400m Hills of England

Twyni Mawr (SN 606 938) - The Welsh P15s

Mainstone Hill (SO 262 880) - The Fours - The 400m Hills of England

Summit Relocations: 

Coed Penllyn (SH 786 696) - 100m Twmpau

Significant Name Changes: 

Grinllwm (SH 772 625) - The Welsh P15s

Mapping Mountains – Hill Reclassifications – The Fours – The 400m Hills of England

Rhos Goch (SO 182 859) – Sub-Four addition

There has been an addition to the listing of the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Rhos Goch (SO 182 859)

The criteria for the list that this addition applies to are:

The Fours – The 400m Hills of England - English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Rhos Goch, and this was derived from the Ordnance Survey Draft Surveyors map, the Ordnance Survey One-Inch ‘Old Series’ map and the 1847 inclosure award, and it is adjoined to the Cilfaesty group of hills, which are situated adjoined to the Welsh border, and it is positioned with minor roads to its north-east, north-west and east, with the B4368 road to its south, and has the village of Ceri (Kerry) towards the north-west.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10^th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop. 

Extract from the Ordnance Survey 1:50,000 Landranger map

Prior to this revision this hill was listed with an estimated c 11m of drop, based on the 439m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and an estimated c 428m col height, based on interpolation of 5m contouring between 425m – 430m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the addition of this hill to Sub-Four status is due to LIDAR analysis, resulting in a 439.1m summit height and a 423.8m col height, with these values giving this hill 15.3m of drop, which is sufficient for it to be classified as a Sub-Four.               

 

The full details for the hill are:

Group:  Cilfaesty

Name:  Rhos Goch

OS 1:50,000 map:  136

Summit Height:  439.1m (LIDAR)

Summit Grid Reference:  SO 18299 85942 (LIDAR)

Col Height:  423.8m (LIDAR)

Col Grid Reference:  SO 18305 86328 (LIDAR)

Drop:  15.3m (LIDAR)

 

For the additions, deletions and reclassifications to The Fours – The 400m Hills of England reported on Mapping Mountains since the December 2013 publication of the 1^st edition of this list by Europeaklist please consult the following Change Registers:

 

The Fours

 

Sub-Fours

 

Myrddyn Phillips and Aled Williams (April 2026)

  

Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales

Pen y Garfan (SN 727 512) – 400m Sub-Pedwar addition

There has been confirmation of a retrospective addition to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Garfan (SN 727 512)

The criteria for the list that this addition applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being included in the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Pen y Garfan, and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-east, west and south, and has the village of Llanddewibrefi towards the north-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 25m of drop, based on the 428m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 403m bwlch height, based on interpolation of 10m contouring between 400m – 410m, and these are the details given the hill when the 1^st edition of the Y Pedwarau, now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in May 2013. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the confirmation of the addition of this hill to 400m Sub-Pedwar status is due to LIDAR analysis, resulting in a 427.4m summit height and a 400.9m bwlch height, with these values giving this hill 26.4m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar.                                         

 

The full details for the hill are:

Group:  Esgair Wen

Name:  Pen y Garfan

OS 1:50,000 map:  146, 147

Summit Height:  427.4m (LIDAR)

Summit Grid Reference:  SN 72700 51270 (LIDAR)

Bwlch Height:  400.9m (LIDAR)

Bwlch Grid Reference:  SN 71962 51672 (LIDAR)   

Drop:  26.4m (LIDAR) 

 

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

 

Y Pedwarau

 

Y Pedwarau – 400m Sub-Pedwarau

 

Y Pedwarau – 390m Sub-Pedwarau

 

Y Pedwarau – 390m Double Sub-Pedwarau

 

Myrddyn Phillips and Aled Williams (April 2026) 

Mapping Mountains – Significant Name Changes – The Welsh P15s

Grinllwm (SH 772 625) 

There has been a Significant Name Change to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Grinllwm (SH 772 625)

The criteria for the list that this name change applies to are:

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

The hill is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its north, south and east, with the B5106 road and the A470 road farther to its east, and has the town of Llanrwst towards the east south-east.

When the listing that became known as The Welsh P15s was being compiled, this hill was listed under the point (Pt. c 264m) notation, with an estimated c 15m of drop, based on an estimated c 264m summit height and the 249m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Since the original compilation of this list there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites, and it is the series of Ordnance Survey Six-Inch maps that form the basis of the change in the listed name of this hill.

The Ordnance Survey series of Six-Inch maps formed the base map Ordnance Survey used for many decades leading to the production of the 1:10,000 Series of maps, both have now been superseded by the digitised Master Map.  The series of Six-Inch maps are excellent for name placement and especially so compared to the contemporary Ordnance Survey 1:25,000 Explorer map, and it is the series of Six-Inch maps that position the name of Grinllwm to land where the summit of this hill is situated.

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the The Welsh P15s is Grinllwm, and this was derived from the Ordnance Survey series of Six-Inch maps. 

 

The full details for the hill are: 

Group:  Carnedd Llywelyn 

Name:  Grinllwm 

Previously Listed Name:  Pt. c 264m 

OS 1:50,000 map:  115

Summit Height:  267.7m (LIDAR)                                                           

Summit Grid Reference:  SH 77258 62516 (LIDAR)                                                  

Bwlch Height:  249.1m (LIDAR) 

Bwlch Grid Reference:  SH 77295 62465 (LIDAR) 

Drop:  18.6m (LIDAR) 

 

Myrddyn Phillips (April 2026) 

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Rhos Swydd (SO 117 650) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Rhos Swydd (SO 117 650)

The criteria for the list that this addition applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Rhos Swydd, and this was derived from the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Fforest Glud group of hills, which are situated in the eastern part of South Wales (Region B, Sub-Region B3), and it is positioned with a minor road to its north-west, the A44 road to its south-west and the A488 road to its south-east, and has the town of Llandrindod towards the south-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 20m of drop, based on an estimated c 267m summit height and an estimated c 247m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the confirmation of the addition of this hill to 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 268.0m summit height and a 244.8m bwlch height, with these values giving this hill 23.2m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Fforest Glud 

Name:  Rhos Swydd 

OS 1:50,000 map:  148

Summit Height:  268.0m (LIDAR) 

Summit Grid Reference:  SO 11706 65038 (LIDAR) 

Bwlch Height:  244.8m (LIDAR) 

Bwlch Grid Reference:  SO 12253 65143 (LIDAR) 

Drop:  23.2m (LIDAR) 

 

Myrddyn Phillips (April 2026)