Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Pt. 372m (SJ 215 551)

There has been a Significant Height Revision to a hill that is listed in the 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 detail on contemporary maps produced from Ordnance Survey data.

The criteria for the list this height revision affects 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 13th May 2017.

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

The hill is being listed by the point (Pt. 372m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its immediate south and the B5430 road to its north, and has the village of Llanarmon-yn-Iâl towards the west north-west.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of this hill was listed as c 375m, based on what was thought to be the uppermost contour that appeared on contemporary Ordnance Survey 1:25,000 Explorer maps.

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

Since publication of these P30 lists on Geoff Crowder’s v-g.me website 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.  This mapping had many more spot heights not on other publicly available Ordnance Survey maps, and for this hill it showed a 372m spot height on the area of its summit.

The summit spot height of 372m on the Ordnance Survey Vector Map Local is not a dramatic height revision when compared to some revised heights, but it does come 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 summit 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, this hill’s new listed summit height is 372m and this was derived from data on the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, this is 3m lower than the interpolated c 375m summit height that was previously given for this hill.

The full details for the hill are:

Group:  Moel y Gamelin

Name:  Pt. 372m

OS 1:50,000 map:  117

Summit Height (New Height):  372m (spot height)

Summit Grid Reference:  SJ 21512 55133 (spot height)

Bwlch Height:  346m (spot height)

Bwlch Grid Reference:  SJ 21519 55047 (spot height)

Drop:  26m (spot height summit and bwlch)

Myrddyn Phillips (December 2020)

Mapping Mountains – Significant Height Revisions – Y Trichant

Pen Rhiw Warren (ST 214 904)

There has been a Significant Height Revision to a hill that is now listed in the Y Trichant, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pen Rhiw Warren (ST 214 904)

The criteria for the listing that this significant height revision applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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.

The name of the hill is Pen Rhiw Warren and its present state is the result of mine spoil, 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 is positioned with the A468 road and the Afon Rhymni (Rhymney River) to its south, the B4251 and A467 roads and the Afon Sirhywi (Sirhowy River) towards the north, and has the town of Caerffili (Caerphilly) towards the west south-west.

This hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh 300m P30 hills were published on Geoff Crowder’s v-g.me website, as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed a bwlch height between 310m – 320m and a broken uppermost contour ring of 320m, therefore it did not meet the criteria used within this list.

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

The details for this hill were re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine and quarry workings, and rail and road cuttings it shows present day continuous contours, as opposed to the broken contours on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  The mapping on OS Maps shows this hill as having eight continuous 5m contour rings, implying that the hill has at least 35m of drop.

Extract from the OS Maps 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.

The summit height produced by LIDAR analysis and its position in relation to the contours shown on the contemporary Ordnance Survey 1:25,000 Explorer map 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.  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 revisions.

Therefore this hill’s new summit height is 350.5m and this was produced by LIDAR analysis, this is a dramatic increase in height and is 30.5m higher compared to the uppermost 320m contour ring on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, but is in accordance with the 5m contouring on the OS Maps website.

The inclusion of this hill to Trichant status and its dramatic increase in height is due to terra-forming by man’s intrusion and is the result of raised mine spoil.  As the hill in its present form is considered solid and stable its inclusion as a Trichant and its increase in known height is accepted as a present-day representation of the land.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Pen Rhiw Warren

OS 1:50,000 map:  171

Summit Height (New height):  350.5m (LIDAR)

Summit Grid Reference:  ST 21463 90441 (LIDAR)

Bwlch Height:  313.9m (LIDAR)

Bwlch Grid Reference:  ST 21869 90427 (LIDAR)

Drop:  36.6m (LIDAR)

Myrddyn Phillips (August 2019)

Mapping Mountains – Significant Height Revisions – Y Trichant

Mynydd y Grug (ST 177 906)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Mynydd y Grug (ST 177 906)

The criteria for the listing that this significant height revision applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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.

The name of the hill is Mynydd y Grug 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 A469 road to its west, the B4251 and the Afon Sirhywi (Sirhowy River) to its north-east and the A468 road to its south, and has the town of Caerffili (Caerphilly) towards the south-west.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 348m summit height, based on the spot height positioned at ST 17688 90958 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; Workings probably obliterated 350c top at ST176908 on 1986 1:50000 map.  As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 348m spot height appears on the 1:25,000 Explorer map.

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

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map became available online and this shows a 375m summit spot height with contemporary Ordnance Survey 1:25,000 Explorer maps showing an uppermost 370m ring contour and a raised summit area which is the bi-product of mine waste spoil.

Extract from the contemporary 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 Mynydd y Grug

The summit height produced by LIDAR analysis and its position in relation to the 348m spot height 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.  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 revisions.

The summit height produced by LIDAR analysis is 374.2m and is positioned at ST 17753 90669, this is a dramatic increase in height over the 348m spot height that appeared on contemporary Ordnance Survey 1:25,000 Explorer maps of the day when the Welsh 300m P30s were first listed, and is 24.2m higher than the uppermost 350m ring contour on contemporary Ordnance Survey 1:50,000 Landranger maps.  However, the 374.2m height produced by LIDAR is in accordance with the uppermost 370m ring contour on contemporary Ordnance Survey 1:25,000 Explorer maps and detail on the OS Maps website.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Mynydd y Grug

OS 1:50,000 map:  171

Summit Height (New height):  374.2m (LIDAR)

Summit Grid Reference:  ST 17753 90669 (LIDAR)

Bwlch Height:  169.85m (LIDAR)

Bwlch Grid Reference:  ST 16783 95144 (LIDAR)

Drop:  204.3m (LIDAR)

Myrddyn Phillips (July 2019)

Mapping Mountains – Significant Height Revisions – Y Trichant and Y Trechol – The Dominant Hills of Wales

Mynydd y Lan (ST 209 923)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant and the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Mynydd y Lan (ST 209 923)

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

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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.

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.

The name of the hill is Mynydd y Lan 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 encircled by roads with the B4251 to its south and west, the A472 to its north and the A467 and B4591 and the Afon Ebwy (Ebbw River) to its east, and has the town of Trecelyn (Newbridge) towards the north and the village of Pontycymer (Crosskeys) towards the east.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 381m summit height, based on the spot height positioned at ST 20794 92508 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map has a 385m spot height positioned at ST 20898 92357.  As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 381m spot height appears on the 1:25,000 Explorer map.

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

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

When the Welsh Dominant list was originally compiled this hill was listed with 56.43% dominance based on its 381m summit spot height and its 166m bwlch spot height, with the latter appearing on the Ordnance Survey 1:25,000 Explorer map, with these values giving this hill 215m of drop.

However, it was not until LIDAR became available that the details for this hill were next 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 Mynydd y Lan

LIDAR bwlch image of Mynydd y Lan

The summit height produced by LIDAR analysis and its position in relation to the 385m spot height 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.  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 revisions.

The summit height produced by LIDAR analysis is 381.3m and is positioned at ST 20903 92337, this is 3.7m lower than the 385m spot height that appears on the Ordnance Survey 1:50,000 Landranger map at approximately the same position.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Mynydd y Lan

OS 1:50,000 map:  171

Summit Height (New height):  381.3m (LIDAR)

Summit Grid Reference:  ST 20903 92337 (LIDAR)

Bwlch Height:  159.5m (LIDAR)

Bwlch Grid Reference:  ST 19806 96725 (LIDAR)

Drop:  221.8m (LIDAR)

Dominance:  58.17% (LIDAR)

Myrddyn Phillips (July 2019)

Mapping Mountains – Significant Height Revisions – Y Trichant

Cefn Llanbister (SO 116 733)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant, and which was initiated by LIDAR analysis and followed by a survey with the Trimble GeoXH 6000 both of which were conducted by Myrddyn Phillips, with the latter taking place on the 03.07.18 in warm and clear conditions.

LIDAR image of Cefn Llanbister

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

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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 its renaming appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Cefn Llanbister and it is placed in the Beacon Hill group of hills, which are situated in the north-eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the Afon Ieithon (River Ithon) and the A 483 road to its west and the B 4356 road to its north, and has the small community of Llanbister at its base to the west of the summit.

As the summit of the hill is a part of open access land it can be approached from most directions with public footpaths accessing this land from the west and east, with the most convenient access to the hill via a track that leaves the B 4356 road just to the north of the summit.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 373m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating 376m at SO GR117732 on 1986 1:50000 map.

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

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the listed height of this hill had been updated to 376m based on the spot height on the Ordnance Survey 1:50,000 Landranger map.

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

The 377.5m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 376m spot height, but does come 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.  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 revisions.

Therefore, this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 377.5m (converted to OSGM15) which is 1.5m higher than its updated height of 376m and 4.5m higher than its original listed height of 373m which appears on the Ordnance Survey 1:25,000 Explorer map.

The Trimble GeoXH 6000 gathering data at the summit of Cefn Llanbister which resulted in this hill's significant height revision

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Beacon Hill

Name:  Cefn Llanbister

OS 1:50,000 map:  136, 148

Summit Height (New height):  377.5m (converted OSGM15)

Summit Grid Reference:  SO 11690 73303

Bwlch Height:  335.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12399 74601

  

Drop:  42.2m (converted to OSGM15)

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (November 2018)