Mapping Mountains – Summit Relocations – 600m Twmpau

600m Twmpau – Summit Relocations

The 600m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 600m and below 700m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 600m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 600m and below 700m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the summit relocations to the main P30 list and the sub list appear below presented chronologically in receding order.

Mapping Mountains - Summit Relocations - 600m Twmpau

Carnedd Llechwedd Llyfn (SH 857 444) - 4th summit relocation

 

There has been a Summit Relocation to a hill that is listed in the Y Pellennig – The Remotest Hills of Wales, The Welsh Highlands – Uchafion Cymru and the 600m Twmpau, 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 Carnedd Llechwedd Llyfn (SH 857 444)

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

Y Pellennig –The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on Mapping Mountains to download in Google Doc format. 

Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams

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

600m Twmpau - Welsh hills at or above 600m and below 700m in height with 30m minimum drop, with an accompanying sub list entitled the 600m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 600m and below 700m in height with 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 available to download in Google Doc format from Mapping Mountains. 

600m Twmpau by Myrddyn Phillips

The name the hill is listed by is Carnedd Llechwedd Llyfn and it is adjoined to the Carnedd y Filiast group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its north-west and north-east, the A5 road farther to its north, the B4407 road farther to its north-west and the A4212 road to its south, and has the town of Y Bala towards the south-east.

When the original list that later became known as the The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 25m of drop, based on the 643m summit spot height positioned at SH 85778 44459 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 618m bwlch height, based on interpolation of 10m contouring between 600m – 610m. 

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

Since the original compilation of these lists 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 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.

The details for this hill were re-assessed 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 Ordnance Survey maps and for this hill it had a twin 643m summit spot height positioned at SH 85789 44665 (latterly shown on the DataMapWales) and a 618m bwlch spot height, with these values giving this hill 25m of drop and resulting in the hill being listed as a twin top. 

Extract from the DataMapWales

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 Carnedd Llechwedd Llyfn (SH 857 444)

The height produced by LIDAR analysis to the summit of this hill is 644.1m and is positioned at SH 85783 44460, whilst LIDAR gives the highest ground adjacent to where the 643m spot height appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map as 643.6m positioned at SH 85785 44677 and SH 85782 44676 and SH 85785 44674 and SH 85779 44667, and 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 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.

Therefore, the new listed summit height of this hill is 644.1m and this is positioned at SH 85783 44460 and this was derived from LIDAR analysis, this position approximately matches that of the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and has resulted in the de-twinning of this hill.

 

The full details for the hill are:

Group:  Carnedd y Filiast

Name:  Carnedd Llechwedd Llyfn

OS 1:50,000 map:  124, 125

Summit Height:  644.1m (LIDAR) 

Summit Grid Reference (New Position):  SH 85783 44460 (LIDAR) 

Bwlch Height:  618.7m (LIDAR) 

Bwlch Grid Reference:  SH 86005 44925 (LIDAR) 

Drop:  25.4m (LIDAR) 

Remoteness:  2.860km

 

Myrddyn Phillips (September 2026) 

Mapping Mountains - Summit Relocations - 600m Twmpau

Cefn yr Ystrad (SO 086 137) - 3rd summit relocation

Summit survey post for Cefn yr Ystrad

Bwlch survey post for Cefn yr Ystrad

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion and the 600m Twmpau with the summit height and its location being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams on the 19^th April 2019.

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

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.

The name of the hill is Cefn yr Ystrad 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 south, with the Pontsticill Reservoir to its west and the Talybont Reservoir towards its north, and has the towns of Aberhonddu (Brecon) towards its north and Merthyr Tudful towards its south.

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

When this hill was first included in the listings that would later become known as the Yr Uchafion and 600m Twmpau the summit position was given to where the 617m map heighted triangulation pillar is situated.  The summit position for this hill was later changed to ground beside the ancient cairn which is named Carn y Bugail.  This summit relocation was based on Abney level surveys that indicated ground at the base of the ancient cairn was 0.8m higher than the flush bracket adjoined to the triangulation pillar.

Thee points were surveyed with the Trimble GeoXH 6000 and these results are given below:

Upright rock beside ancient cairn:  616.888m at SO 08810 13628

Grass at base of ancient cairn:  616.311m at SO 08793 13627

Small embedded rock beside trig pillar:  617.442 at SO 08696 13729

Gathering data on the upright rock beside the ancient cairn of Carn y Bugail

The 617.4m summit height produced by the Trimble GeoXH 6000 survey and its position in relation to the previously listed summit position on ground at the base of the ancient cairn comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

Gathering data at the base of the ancient cairn 

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 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. 

Gathering data at the highest embedded rock beside the triangulation pillar

The summit height produced by the Trimble GeoXH 6000 survey is 617.4m and is positioned at SO 08696 13729, this position is approximately 140 metres north-west from where the old listed summit is positioned.

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Cefn yr Ystrad

OS 1:50,000 map:  160

Summit Height:  617.4m (converted to OSGM15)

Summit Grid Reference (new position):  SO 08696 13729

  

Bwlch Height:  439.9m (converted to OSGM15)

Bwlch Grid Reference:  SO 05261 17241

Drop:  177.5m (converted to OSGM15)

For details on the survey that relocated the summit of this hill

Myrddyn Phillips and Aled Williams (August 2019)

Mapping Mountains - Summit Relocations - 600m Twmpau

Foel Cedig (SH 981 283) - 2nd summit relocation

Survey post for Foel Cedig

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion, the 600m Twmpau and Y Pellennig – The Remotest Hills of Wales with the summit height, its location and drop of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips with the bwlch surveyed on the 19^th October 2016 and the summit on the 16^th August 2018.

Foel Cedig (SH 981 283) on the left and Cyrniau Nod (SH 988 279) on the right

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

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.

Y Pellennig – The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop, the list is a joint compilation between Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on the Mapping Mountains site in Google Doc format.

The name of the hill is Foel Cedig, and it is adjoined to the Y Berwyn range of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and is positioned to the north of Llyn Efyrnwy (Lake Vyrnwy) and has the town of Y Bala towards the north-west.

As the summit of the hill is a part of designated open access land it can be approached from various directions.  However, the easiest approach is from the north-west where a track contours the moorland and it is only a short walk from this point to the summit of the hill.

When the qualifying summit for the Yr Uchafion, 600m Twmpau and Y Pellennig – The Remotest Hills of Wales was first listed it was given to the hill named Cyrniau Nod which is positioned at SH 988 279 and listed with a 666m summit height which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.  Whilst the summit of Foel Cedig which is positioned at SH 981 283 is given a 666m height on these same maps.

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

As the surveying technique that produced these two  spot heights has a +/- 3m margin of uncertainty applied to it, it meant that Foel Cedig could in fact be higher than Cyrniau Nod, therefore both hills were surveyed with the Trimble GeoXH 6000.

The results from these two surveys are given below:

  

Foel Cedig:  667.417m at SH 98170 28327

Cyrniau Nod:  666.207m at SH 98847 27920

Since the qualifying summit has been relocated to Foel Cedig this has also affected the lists of Marilyns, Humps, Simms, Hewitts, Nuttalls and Tumps, with Alan Dawson as list author of the Marilyns, Simms and Hewitts having accepted this result the other list authors soon followed suit.

A subsequent Leica GS15 survey conducted by John Barnard and Graham Jackson on the 15^th September 2018 resulted in the following:

Foel Cedig:  667.479m at SH 98170 28327

Cyrniau Nod:  666.234m at SH 98847 27918

Data sets of ten and eleven minutes were collected with the Trimble GeoXH 6000, whilst 122 and 121 minute data sets were collected with the Leica GS15.

The Trimble GeoXH 6000 gathering data at the summit of Foel Cedig with Cyrniau Nod in the background

The 667.4m summit height produced by the Trimble GeoXH 6000 survey and its position in relation to that of Cyrniau Nod 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 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.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The Trimble GeoXH 6000 gathering data at the summit of Cyrniau Nod with Foel Cedig in the background on the left

The summit height produced by the Trimble GeoXH 6000 survey is 667.4m and is positioned at SH 98170 28327, this position is approximately 800 metres north-west from where the old listed summit of Cyrniau Nod is positioned.

The full details for the hill are:

Group:  Y Berwyn

Name:  Foel Cedig

OS 1:50,000 map:  125

Summit Height:  667.4m (converted to OSGM15)

Summit Grid Reference (new position):  SH 98170 28327

  

Bwlch Height:  487.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 94458 27324

Drop:  180.0m (converted to OSGM15)

Remoteness:  3.200 km

For details on the survey that relocated the summit of this hill

Myrddyn Phillips (January 2019)

Mapping Mountains - Summit Relocations - 600m Twmpau

Cefn Gwyntog (SH 975 266) - 1st summit relocation

Survey post for Cefn Gwyntog

There has been a Summit Relocation to a hill that is listed in the Yr Uchafion and the 600m Twmpau, with the summit height and drop of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips which took place on the 16^th August 2018.

Cefn Gwyntog (SH 975 266)

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

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.

The name of the hill is Cefn Gwyntog, and it is adjoined to the Y Berwyn range of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned to the north of Llyn Efyrnwy (Lake Vyrnwy) and has the town of Y Bala towards the north north-west.

As the summit of the hill is a part of designated open access land it can be approached from various directions.  However, the easiest approach is from the north where a track contours the moorland and a narrow path leaves this track toward an old gate and continues toward the summit of this hill.

When this hill was first included in the lists that would later be known as the Yr Uchafion and the 600m Twmpau the summit position was given to where the 615m spot height appeared on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day, this is at SH 97602 26597.  This position is close to where a small cairn with an upright stone is placed on the ground.

However, having visited this summit 19 times prior to the survey with the Trimble GeoXH 6000 I knew that there were two other positions that vied for the highest point of this hill, and therefore I wanted to conduct three separate surveys from the area of its summit.

The results from these three surveys are given below:

1^st survey:  613.766m at SH 97596 26696

2^nd survey:  613.299m at SH 97604 26598

3^rd survey:  613.104m at SH 97655 26618

The first survey was to featureless ground two metres from where the narrow path crosses the summit area of this hill.

Gathering data at the summit of Cefn Gwyntog with the old summit position in the right background of this photograph

The second survey was to the highest ground close to where the small cairn with an upright stone is placed, and within two metres matches the position of the 615m spot height.

Gathering data during the second summit survey on Cefn Gwyntog with the new summit position of this hill in the left centre background of this photograph

The third survey was to ground beside a small cairn on the eastern part of the uppermost 610 metre ring contour that appears on contemporary Ordnance Survey maps.

Gathering data during the third summit survey on Cefn Gwyntog

The 613.8m summit height produced by the Trimble GeoXH 6000 survey and its 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 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.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the new summit position in relation to where the spot height is positioned. 

The summit height produced by the Trimble GeoXH 6000 survey is 613.8m and is positioned at SH 97596 26696, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 100 metres north from where the old listed summit is positioned.

The full details for the hill are:

Group:  Y Berwyn

Name:  Cefn Gwyntog

OS 1:50,000 map:  125

Summit Height:  613.8m (converted to OSGM15)

Summit Grid Reference (new position):  SH 97596 26696

  

Bwlch Height:  587.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 97493 27338

Drop:  26.7m (converted to OSGM15)

For details on the survey that confirmed the summit relocation of this hill

Myrddyn Phillips (January 2019)