Mapping Mountains – Summit Relocations – The Welsh P15s

Cefn Gwrhyd (SN 737 096) 

There has been a Summit Relocation to a hill that is listed in the 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 Cefn Gwrhyd (SN 737 096)

The criteria for the list that this summit relocation 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 name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A474 road to its west, the A4067 road to its south-east and a minor road to its immediate east, and has the community of Y Gurnos towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included as with a 291m spot height in the vicinity of its summit and bwlch contouring between 280m – 290m that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, it was judged not to meet the criterion for the main P15 or the accompanying P14 sub list.  With an interpolated summit position later noted to an ancient cairn at SN 73735 09589. 

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

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and for this hill a 300m summit spot height is given. 

Extract from the interactive mapping hosted on the WalkLakes website

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 Cefn Gwrhyd (SN 737 096)

LIDAR analysis gives the highest ground on this hill as 300.5m positioned at SN 73765 09682, and this position 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 of the hill 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 300.5m and this is positioned at SN 73765 09682, 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 93 metres north north-eastward from where the ancient cairn is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Cefn Gwrhyd 

OS 1:50,000 map:  160

Summit Height:  300.5m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 73765 09682 (LIDAR) 

Bwlch Height:  283.1m (LIDAR) 

Bwlch Grid Reference:  SN 73543 09172 (LIDAR) 

Drop:  17.3m (LIDAR) 

 

Myrddyn Phillips (June 2024)

 

 

  

Mapping Mountains – Significant Height Revisions – The Welsh P15s

Cefn Gwrhyd (SN 737 096) 

There has been a Significant Height Revision 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 Cefn Gwrhyd (SN 737 096)

The criteria for the list that this height revision 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 name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A474 road to its west, the A4067 road to its south-east and a minor road to its immediate east, and has the community of Y Gurnos towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included as with a 291m spot height in the vicinity of its summit and bwlch contouring between 280m – 290m that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, it was judged not to meet the criterion for the main P15 or the accompanying P14 sub list. 

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

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and for this hill a 300m summit spot height is given. 

Extract from the interactive mapping hosted on the WalkLakes website

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 Cefn Gwrhyd (SN 737 096)

The summit height produced by LIDAR analysis is 300.5m and when compared to detail on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, 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 or Harvey 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 to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 300.5m and this was derived from LIDAR analysis.  This is 9.5m higher than the 291m spot height and 5.5m higher than the estimated c 295m summit height if based on interpolation of the uppermost contour on the contemporary Ordnance Survey 1:25,000 Explorer map. 

 ills of Wales, and are reproduced below@

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Cefn Gwrhyd 

OS 1:50,000 map:  160

Summit Height (New Height):  300.5m (LIDAR)                                                           

Summit Grid Reference:  SN 73765 09682 (LIDAR) 

Bwlch Height:  283.1m (LIDAR) 

Bwlch Grid Reference:  SN 73543 09172 (LIDAR) 

Drop:  17.3m (LIDAR) 

 

Myrddyn Phillips (June 2024)

 

 

 

 

 

 

 

  

Mapping Mountains – Hill Reclassifications – The Welsh P15s

 

Cefn Gwrhyd (SN 737 096) – Welsh P15 addition 

There has been an addition to the list of 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 Cefn Gwrhyd (SN 737 096)

The criteria for the list that this addition 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 name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A474 road to its west, the A4067 road to its south-east and a minor road to its immediate east, and has the community of Y Gurnos towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included as with a 291m spot height in the vicinity of its summit and bwlch contouring between 280m – 290m that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, it was judged not to meet the criterion for the main P15 or the accompanying P14 sub list. 

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

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and for this hill a 300m summit spot height is given.

Extract from the interactive mapping hosted on the WalkLakes website

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 Welsh P15 status is due to LIDAR analysis, resulting in a 300.5m summit height and a 283.1m bwlch height, with these values giving this hill 17.3m of drop, which is sufficient for it to be included in the main list of The Welsh P15s. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Cefn Gwrhyd 

OS 1:50,000 map:  160

Summit Height:  300.5m (LIDAR)                                                           

Summit Grid Reference:  SN 73765 09682 (LIDAR) 

Bwlch Height:  283.1m (LIDAR) 

Bwlch Grid Reference:  SN 73543 09172 (LIDAR) 

Drop:  17.3m (LIDAR) 

 

Myrddyn Phillips (May 2024)

 

 

 

Mapping Mountains – Hill Reclassifications – Y Trichant - The 300m Hills of Wales

Cefn Gwrhyd (SN 73107 08600 and SN 73109 08601) – Sub-Trichant reclassified to Trichant

There has been a reclassification to the list of Y Trichant – The 300m 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 Cefn Gwrhyd (SN 731 086)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list subsequently appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Cefn Gwrhyd, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A474 road to its west, the A4068 road to its north and the A4067 road to its south-east, and has the town of Pontardawe towards the south, and the villages of Brynaman towards the north and Ystalyfera towards the east.  

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill appeared in the accompanying Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list.

When 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 an estimated c 29m of drop, based on an estimated c 303m summit height and an estimated c 274m bwlch height, with each based on interpolation of 10m contouring.

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website 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.

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 304m summit spot height and a 275m bwlch spot height, with these values giving this hill 29m of drop.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the summit spot height

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website showing the spot height on the area of this hill's bwlch

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 reclassification of this hill from Sub-Trichant status is due to LIDAR analysis, resulting in a 305.5m summit height and a 274.8m bwlch height, with these values giving this hill 30.7m of drop, which is sufficient for it to be classified as a Trichant. 

The full details for the hill are:

Group:  Mynydd Du

Name:  Cefn Gwrhyd

OS 1:50,000 map:  160

Summit Height:  305.5m (LIDAR)

Summit Grid Reference:  SN 73107 08600 and SN 73109 08601 (LIDAR)

Bwlch Height:  274.8m (LIDAR)

Bwlch Grid Reference:  SN 73885 09967 (LIDAR)

Drop:  30.7m (LIDAR)

Myrddyn Phillips (March 2019)