Mapping Mountains – Summit Relocations – 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru

 

Yr Eifl (SH 364 447) 

There has been a Summit Relocation that is retrospective to a hill that is listed in the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop, the dominance and status of the hill derived from a Leica GS15 summit survey conducted by John Barnard, Graham Jackson and Myrddyn Phillips, and LIDAR bwlch analysis conducted by Aled Williams.

Yr Eifl (SH 364 447)

The criteria for the three listings that this summit relocation applies to are: 

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m 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. 

500m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

 

Y Trechol - The Dominant Hills of Wales 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. 

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Yr Eifl and it is adjoined to its own 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-east, the B4417 road to its south and the A499 road to its east, and has the villages of Trefor towards the north north-east and Llithfaen towards the south south-west.

When the listings of the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru were first compiled, this hill was listed with a summit height of 564m, based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

However, it was not until the survey with the Leica GS15 that the details for this hill could be accurately re-assessed.  Although the trig pillar is positioned on a relatively stable base it is positioned on the top of a substantial ancient cairn which consists of a multitude of individual stones and rocks and as this is considered as not being permanent in nature, it is the highest remaining natural ground on the periphery of the ancient cairn that is taken as both its listed summit height and summit position, and when compared to its originally listed summit position this comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

 

Gathering data with the Leica GS15 at the listed summit position of Yr Eifl

Therefore, the summit height produced by the Leica GS15 survey is 560.7m and this is positioned at SH 36482 44734.  This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, although this position is relatively close to where the triangulation pillar is situated, it is importantly positioned to the highest remaining natural ground on the periphery of the large ancient cairn.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Yr Eifl

Name:  Yr Eifl

OS 1:50,000 map:  123

Summit Height:  560.7m (converted to OSGM15, Leica GS15)

Summit Grid Reference (New Position):  SH 36482 44734 (Leica GS15)  

Bwlch Height:  129.4m (LIDAR)

Bwlch Grid Reference:  SH 45347 48678 (LIDAR)

Drop:  431.3m (Leica GS15 summit and LIDAR bwlch)

 

Myrddyn Phillips and Aled Williams (March 2026)

Mapping Mountains – Summit Relocations – 500m Twmpau and Welsh Highlands – Uchafion Cymru

 

Mynydd Trawsnant (SN 824 485) 

There has been a Summit Relocation to a hill that is listed in the 500m Twmpau and 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 Mynydd Trawsnant (SN 824 485)

The criteria for the two listings that this summit relocation applies to are:

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m 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.

The 500m Twmpau by Myrddyn Phillips

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.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Trawsnant and it is adjoined to the Drygarn Fawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west and the A483 road to its south-east, and has the town of Llanwrtyd towards the east south-east. 

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

When the original list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 139m of drop based on the 517m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 82136 48415, and an estimated c 378m bwlch height. 

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

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 378m bwlch spot height and therefore its drop was amended to 139m. 

LIDAR summit image of Mynydd Trawsnant (SN 824 485)

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. 

Extract from the Ordnance Survey series of Six-Inch maps

The details ascertained from LIDAR for the new and old summit position are given below, but as the upper section of this hill is forested the accuracy of LIDAR modelling may be compromised.  However, the pre-forestry levelled height on the Ordnance Survey series of Six-Inch maps substantiates the new LIDAR position. 

 

New summit:  516.559m at SN 82452 48564 

Old summit:  516.489m at SN 82162 48430 

 

The above detail compared to the summit position previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies to when the high point is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist. 

Therefore, the summit height produced by LIDAR analysis is 516.6m and this is positioned at SN 82452 48564.  This position is not given a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map, but is close to where the 517m spot height appears on the contemporary 1:50,000 Landranger map and is approximately 320 metres north-eastward from where the previously listed summit is positioned.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Drygarn Fawr

Name:  Mynydd Trawsnant

OS 1:50,000 map:  147

Summit Height:  516.6m (LIDAR)

Summit Grid Reference (new position):  SN 82452 48564 (LIDAR)  

Bwlch Height:  378.3m (LIDAR)

Bwlch Grid Reference:  SN 82781 50423 (LIDAR)

Drop:  138.3m (LIDAR)

 

Myrddyn Phillips and Aled Williams (August 2023)

 

 

 

 

 

 

Mapping Mountains – Summit Relocations – 500m Twmpau and Welsh Highlands – Uchafion Cymru

Foel Fawr (SH 728 392)

There has been a Summit Relocation to a hill that is listed in the 500m Twmpau and the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams on the 19^th July 2020.

Foel Fawr (SH 728 392)

The criteria for the two listings that this summit relocation applies to are:

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m 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.

The 500m Twmpau by Myrddyn Phillips

Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

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

The name the hill is listed by is Foel Fawr and it is adjoined to the Arenig Fach 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 B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Trawsfynydd towards the south-west.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 41m of drop based on the 528m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SH 72620 39472, and an estimated c 487m bwlch height, based on interpolation of 10m contouring between 480m - 490m.

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

Since first compilation of the Welsh 500m P15 list there have been a number of Ordnance Survey 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 are current and 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, and it was this map that showed a 528m map heighted twin summit positioned at SH 72873 39268.  The two 528m spot heights are also shown on the mapping hosted on the Magic Maps website.

Extract from the Magic Maps website

However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.  The height and position for each summit is given below:

South-easterly summit:  528.611m at SH 72872 39284

North-westerly summit:  527.542m at SH 72621 39476

The above detail compared to the prioritised summit previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the listing of a new twin summit or de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Gathering data at the higher of the Foel Fawr summits

Gathering data at the lower of the Foel Fawr summits

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 528.6m and this is positioned at SH 72872 39284, this position is not given a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, but is given a 528m spot height on the interactive mapping hosted on the Magic Maps website, and is approximately 260 metres south-eastward from where the previously listed and prioritised summit is positioned.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Arenig Fach

Name:  Foel Fawr

OS 1:50,000 map:  124

Summit Height:  528.6m (converted to OSGM15)

Summit Grid Reference (New Position):  SH 72872 39284

  

Bwlch Height:  485.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 73074 39525

Drop:  43.1m

Myrddyn Phillips and Aled Williams (October 2020)

Mapping Mountains – Summit Relocations – 500m Twmpau and The Welsh Highlands – Uchafion Cymru

Carreg Croes Ifor (SO 248 106)

There has been a Summit Relocation to a hill that is listed in the 500m Twmpau and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 summit survey conducted by Aled Williams.

LIDAR image of Carreg Croes Ifor (SO 248 106)

The criteria for the two listings that this summit relocation applies to are:

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m 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.

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

The name the hill is listed by is Carreg Croes Ifor and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road to its north, the B4248 road to its south-west and the B4246 road to its east, and has the town of Blaenafon towards the south south-east.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 18m of drop based on a non-interpolated c 500m summit height and a 482m bwlch height taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

Since first compilation of the Welsh 500m P15 list there are a number of maps now available online, and the details for this hill were re-assessed when the Ordnance Survey 1:25,000 Historical map became available online, and this map gives a 1657ft (505.1m) summit spot height for this hill.

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

The imperial height on the Ordnance Survey 1:25,000 Historical map is derived from a 1657.4m (505.2m) Surface Height that appears on the Ordnance Survey series of Six-Inch maps.  Therefore, the summit height for this hill was revised and listed as 505m with the caveat that since this height was derived this hill has undergone mining activity which has substantially altered the landscape.

Extract from the Ordnance Survey series of Six-Inch maps

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 for Carreg Croes Ifor

The summit height and position produced by LIDAR analysis is 509.8m at SO 24848 10663, and this position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

During analysis of this hill, Aled used overlays from old maps with contemporary maps and the details produced via LIDAR.  This shows that the natural 505.2m summit positioned at SO 24810 10620 is now under a substantial amount of mine spoil and this has raised the height of the summit. 

The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and as the natural summit is now under a spoil tip and an on-site visit confirms this artificially raised summit to be solid and stable, it is the Trimble summit height and position that is being prioritised for this hill.     

Therefore, the new listed summit height for this hill is 509.7m and is positioned at SO 24848 10663, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 160 metres westward from where the previously listed summit is positioned. 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Carreg Croes Ifor

OS 1:50,000 map:  161

Summit Height:  509.7m (converted to OSGM15, Trimble GeoXH 6000, artificially raised)

Summit Grid Reference (New Position):  SO 24848 10663 (Trimble GeoXH 6000) 

 

Bwlch Height:  482.1m (LIDAR)

Bwlch Grid Reference:  SO 25485 10565 (LIDAR)

Drop:  27.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Aled Williams and Myrddyn Phillips (May 2020)