Tuesday, 31 October 2017

Mapping Mountains – Hill Reclassifications – Humps


Foel Fras (SN 765 926) – Prioritised Twin Hump deletion

This is the twenty fourth in a series of Hill Reclassification posts that detail hills whose status has been altered in the listing of the Humps (HUndred Metre Prominences) through map study and / or surveys that I have instigated.

Foel Fras (SN 765 926) on right of photo

This and forthcoming posts are retrospective as many of these hill reclassifications were initiated from studying the Ordnance Survey enlarged mapping that is hosted on the Geograph website, or in this instance from a survey with the Trimble GeoXH 6000, and for the reclassifications that affected the Humps the survey of this hill took place on the 18.05.14.

The listing of Humps was published in book format by Lulu in 2009 and entitled More Relative Hills of Britain, its author; Mark Jackson gives credit to a number of people who contributed toward the formation of this list, these include; Eric Yeaman, Alan Dawson, Clem Clements, Rob Woodall, Bernie Hughes, Pete Ridges and others.  When the list was published in book format there were 2987 Humps listed with their criteria being any British hill that has 100m or more of drop, accompanying the main list is a sub category entitled Subhumps, with the criteria being any British hill that has 90m or more and below 100m of drop.

More Relative Hills of Britain by Mark Jackson

The details for the reclassification appear below:

There has been a reclassification to the listing of the Humps (HUndred Metre Prominences) instigated by a survey with the Trimble GeoXH 6000 which took place on the 18.05.14.

Mark Jackson had originally listed this hill with c 105m of drop based on the 529m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 424m based on bwlch contouring at 10m intervals.  This hill was listed as a prioritised Twin Hump along with two other non-prioritised Twin Hump 529m summit spot heighted hills which are positioned at SN 764 943 and SN 765 920.  Therefore, prior to the survey with the Trimble GeoXH 6000 this hill was listed as a prioritised Twin Hump.  
   
The hill is adjoined to the Pumlumon group of hills and is situated between the A 489 road to the north and the A 44 road to the south, and is positioned between the town of Machynlleth towards the north and the small community of Ffwrnais (Furnace) towards the west.

This hill and its adjacent twin map heighted summits were surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips on the 18.05.14 resulting in a 528.7m (converted to OSGM15) summit height, which proved lower than the 529.4m (converted to OSGM15) summit at SN 764 943, with the other summit being 528.3m (converted to OSGM15) at SN 765 920, with this survey confirming this hill’s deletion from prioritised Twin Hump status with 67.6m of drop.

The deletion of this hill from prioritised Twin Hump status was accepted by Mark Jackson and it was removed from the listing of the Humps on 22.09.14.

Gathering data with the Trimble GeoXH 6000 at the summit of Foel Fras

The full details for the hill are:

Name:  Foel Fras

Summit Height:  528.7m (converted to OSGM15)

OS 1:50,000 map:  135

OS 1:25,000 map:  23, 215

Summit Grid Reference:  SN 76548 92610 (as listed in the Humps)

Drop:  67.6m (converted to OSGM15)


Myrddyn Phillips (October 2017)


Sunday, 29 October 2017

Mapping Mountains – Significant Height Revisions – Y Trichant


Y Trichant – Significant Height Revisions

Y Trichant are the Welsh hills at or above 300m and below 40om in height that have a minimum drop of 30m, with these hills forming the 300m height band within the listing of the Twmpau (thirty welsh metre prominences and upward).  Accompanying the main P30 list is a sub list entitled the 300m Sub-Trichant with the qualification to 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, with the Introduction to the re-naming of this list and its publication history appearing on Mapping Mountains on 13.05.17.

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








Mapping Mountains - Significant Height Revisions - Y Trichant

Pen y Bigil (SH 576 621) - 11th significant height revision

Survey post for Pen y Bigil

Hill Reclassifications post for Pen y Bigil


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 a subsequent survey with the Trimble GeoXH 6000 both of which were conducted by Myrddyn Phillips, with the latter taking place on the 06.10.18.

Pen y Bigil (SH 576 621)

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 the renaming of it appearing on Mapping Mountains on the 13th May 2017.

The name of the hill is Pen y Bigil and it is adjoined to the Glyderau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the A4244 road to its north-west and the A4086 road and Llyn Padarn to its south, and has the villages of Deiniolen towards the north and Llanberis towards the south.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list as it was thought not to meet the criteria then used for the main P30 list; however this sub list has now been standardised and interpolated heights and drop values also included in the main P30 and the accompanying sub list.
                                      
When this list was standardised and interpolated heights also included this hill was listed with an estimated c 33m of drop, based on an estimated c 326m summit height and an estimated c 293m bwlch height, with each based on interpolation of 5m contouring on the contemporary Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-assessed when the Ordnance Survey 1:25,000 historical map and the series of Six-Inch maps became available online, the former has a 1081ft height and the latter has a 1080ft height given to this hill’s summit, these heights equate to 329m in metric, and when coupled with the c 293m estimated bwlch height gives this hill c 36m of drop.

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

Extract from the Ordnance Survey series of Six-Inch maps

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, and soon after analysing this hill with LIDAR it was surveyed with the Trimble GeoXH 6000. 

LIDAR image of Pen y Bigil

The 331.0m summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 329m 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 331.0m which is 2m higher than its updated height of 329m that appears as an imperial height on the Ordnance Survey 1:25,000 historical map and the series of Six-Inch maps, and 5m higher than its previously estimated height of c 326m.

The Trimble GeoXH 6000 gathering data at the summit of Pen y Bigil

The full details for the hill are:

Group:  Glyderau

Name:  Pen y Bigil

OS 1:50,000 map:  114, 115

Summit Height (new height):  331.0m (converted to OSGM15)

Summit Grid Reference:  SH 57600 62119

Bwlch Height:  292.6m (LIDAR)

Bwlch Grid Reference:  SH 58014 62043 (LIDAR) 

Drop:  38.4m (Trimble summit and LIDAR bwlch)



Myrddyn Phillips (March 2019)






Mapping Mountains - Significant Height Revisions - Y Trichant

Cefn Llanbister (SO 116 733) - 10th significant height revision

Survey post for Cefn Llanbister

Summit Relocation post for Cefn Llanbister


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 13th 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

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)



Myrddyn Phillips (November 2018)






Mapping Mountains - Significant Height Revisions - Y Trichant

Upper Park (SJ 189 052) - 9th significant height revision

Survey post for Upper Park

Summit Relocation post for Upper Park


There has been a Significant Height Revision to a hill that is listed in the Y Trichant and Y Trechol – The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 7th January 2018.

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

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for 
Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Upper Park and it is situated in the Carnedd Wen range of hills which are in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned between the A 458 road to its north and the A 483 road to its south-east, and has the town of Y Trallwng (Welshpool) to its north-east.

As the summit of the hill is not on designated open access land and is part of a private estate permission to visit should be sought, for those wishing to do so there are a number of options for an ascent, all of which use tracks through forested plantations.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was originally listed as 352m, with this taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, latterly the hill has been listed with an estimated c 353m summit height.

The 354.0m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 352m 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 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, and also hill’s that do not possess a summit spot height and whose estimated summit height has a 2m or more discrepancy when compared to data produced either by the Trimble or by LIDAR.  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 354.0m (converted to OSGM15) which is 2.0m higher than the 352m spot height that appears on the Ordnance Survey 1:25,000 Explorer map.


The full details for the hill are:

Group:  Carnedd Wen

Summit Height (New Height):  354.0m (converted to OSGM15)

Name:  Upper Park

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 18980 05270 
        
Drop:  177.0m (converted to OSGM15)

Dominance:  49.998%


The Trimble GeoXH 6000 gathering data at the summit of Upper Park (SJ 189 052) which resulted in this hill's significant height revision


Myrddyn Phillips (February 2018)






Mapping Mountains - Significant Height Revisions - Y Trichant

Mynydd yr Heol (SO 107 601) - 8th significant height revision

Survey post for Mynydd yr Heol

Hill Reclassifications post for Mynydd yr Heol


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Trichant, with the survey that resulted in this height revision conducted on the 3rd October 2017.

The criteria for the listing this height revision affects are:

Y Trichant – Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming was published on Mapping Mountains on the 13th May 2017.

The name of the hill is Mynydd yr Heol and it is situated in the Fforest Glud range of hills which are in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and the hill is positioned between the town of Llandrindod (Llandrindod Wells) to its west and the small community of Hundred House to its south.

The grazed summit of Mynydd yr Heol (SO 107 601)

As the summit of the hill is not on designated open access land permission to visit should be sought, for those wishing to do so the nearest public footpath is south of the summit and it passes over the bwlch of the hill in a west – east direction.  However, the easiest and most convenient ascent is from the east following a green track up the hill from the convenience of a minor lane.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 382m, with this taken from the summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

The 386.8m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is a dramatic increase from the previously listed summit height of 382m, and therefore it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, or a previous estimated summit height based on contour interpolation.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  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 of this hill is easily identified and consists of closely cropped grass at the top of a field used for grazing.  Just below the summit to the south-west is a small, but steep section of exposed rock, similar to an old quarry, otherwise the summit area is not remarkable, except of course for its dramatic increase in known height.

Therefore, this hill’s new summit height is 386.8m (converted to OSGM15) which is 4.8m higher than its previously listed height of 382m which is shown on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.


The full details for the hill are:

Cardinal Hill:  Gilwern Hill

Summit Height (New Height):  386.8m (converted to OSGM15)

Name:  Mynydd yr Heol

OS 1:50,000 map:  148

Summit Grid Reference:  SO 10793 60177  
       
Drop:  31.2m (converted to OSGM15)


Gathering data with the Trimble GeoXH 6000 from the summit of Mynydd yr Heol which resulted in this hill's significant height revision


Myrddyn Phillips (December 2017)







Mapping Mountains - Significant Height Revisions - Y Trichant

Teisen Priodas (SN 820 108) - 7th significant height revision

Survey post for Teisen Priodas

Hill Reclassifications post for Teisen Priodas

Significant Name Changes post for Teisen Priodas


There has been a Significant Height Revision to a hill that is now listed in the Y Trichant due to analysis of LIDAR data by Kevin McGovern and also independently by Aled Williams and George Gradwell, which was subsequently confirmed by a survey with the Trimble GeoXH 6000 that was conducted on the 13th June 2017. 

Y Trichant is the title for the hills in the 300m height band of the Twmpau (thirty welsh metre prominences and upward) and takes in all Welsh hills at or above 300m and below 400m in height that have a minimum 30m of drop, with the introduction to the re-naming of this list appearing on Mapping Mountains on the 13th May 2017.

The ridge that this hill is a part of is named Mynydd y Drum and it consists of three listed hills, one being a sub hill which is deemed natural, and two being P30s that are the consequence of mine workings, with one of these P30s having been fully landscaped.  It is this fully landscaped P30 whose details are given in this article.  

When visiting this hill I made place-name enquiries with two of the remaining six mine workers and was told that the name the hill is known by is Teisen Priodas, which translated into English means the wedding cake, an apt name as the hill has three tiers and is relatively flat on top.

Teisen Priodas is adjoined to the Fforest Fawr group, with its Cardinal Hill being Fan Gyhirych (SN 880 191) and is placed in the Region of South Wales (Region C, Sub-Region C2), with the hill positioned between the small communities of Abercraf (Abercrave) to the north and Y Coelbren towards the east.

As the hill is a part of the Nant Helen Opencast Mine permission to visit should be sought, however Ordnance Survey maps still show public footpaths crossing the opencast workings with the nearest one placed just to the west of the summit and crossing land associated with the mine from a south to a north direction, this public footpath is probably on a part of land that has been landscaped.

Teisen Priodas consists of waste spoil that is now landscaped, and as it is customary for Ordnance Survey maps to show mine workings without any form of contour line the hill had not been classified prior to the analysis of LIDAR data, although the area of this hill’s bwlch does possess contours.  The mine is situated on the north-eastern part of the Mynydd y Drum ridge, with the south-western part of this broad ridge still intact having not been mined and possessing a 200m Sub-Twmpau that is listed by the name of Mynydd y Drum.

The highest ring contour shown on Ordnance Survey 1:25,000 Explorer maps for the whole  broad ridge of Mynydd y Drum is 290m which appears on the south-western part of this ridge where the 296.2m summit of the Sub-Twmpau is situated at SN 80718 09753, and also at the eastern periphery of the mine at SN 833 112.  

The survey with the Trimble GeoXH 6000 produced a summit height for Teisen Priodas of 337.9m (converted to OSGM15) which comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, or a previous estimated summit height based on interpolation of contours.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 map for detailing these revisions.

The summit area of this hill is now landscaped and relatively flat and expansive, with the high point toward the eastern part of the summit plateau which consists of long grasses.

Therefore this hill’s new summit height is 337.9m (converted to OSGM15), as no summit contours exist for this hill above the 290m given to the far eastern part of the mine workings on the Ordnance Survey 1:25,000 Explorer map, this is a dramatic 47.9m increase in height compared to its uppermost ring contour. 


The full details for the hill are:

Cardinal Hill:  Fan Gyhirych 

Summit Height (New Height):  337.9m (converted to OSGM15)

Name:  Teisen Priodas

OS 1:50,000 map:  160

Summit Grid Reference:  SN 82013 10833
         
Drop:  93.3m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Teisen Priodas (SN 820 108) which confirmed this hill's significant height revision



Myrddyn Phillips (August 2017)






Mapping Mountains - Significant Height Revisions - Y Trichant

Moel Llaethbwlch (SJ 113 167) - 6th significant height revision

Survey post for Moel Llaethbwlch


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Trichantwith the survey that resulted in this height revision conducted on the 6th April 2017.

The criteria for the listing that this height revision affects are:

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming was published on Mapping Mountains on the 13th May 2017.

The name of the hill is Moel Llaethbwlch and it is situated in the Y Berwyn range of hills which are in the south-east part of North Wales, and the hill is positioned between the town of Llanfyllyn to the north-east and the village of Meifod to the south-east.

As the summit of the hill is not a part of designated open access land permission to visit should be sought, with the nearest public footpaths contouring round the hill’s northern lower slopes and also its lower southern slopes.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as c 370m based on the small uppermost 370m ring contour on Ordnance Survey 1:25,000 Explorer maps, and to my knowledge no spot height has ever appeared on an Ordnance Survey map for this hill.

The 372.1m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic increase from the previously estimated summit height of c 370m, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, or a previous estimated summit height based on contour interpolation.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 map for detailing these revisions.

The summit of this hill is easily identified and consists of closely cropped grass at the top of a field used for grazing.  Although the immediate summit area is relatively flat it is encircled by what looks like the remains of a small hill fort, although I have found no evidence to support this.

Therefore this hill’s new summit height is 372.1m (converted to OSGM15) which is 2.1m higher than its previously estimated height of c 370m and also 2.1m higher than its 370m uppermost ring contour on Ordnance Survey maps.


The full details for the hill are:

Cardinal Hill:  Moel y Fronllwyd

Summit Height (New Height):  372.1m (converted to OSGM15)

Name:  Moel Llaethbwlch

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 11335 16724
          
Drop:  43.3m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Moel Llaethbwlch (SJ 113 167)  which resulted in this hill's significant height revision


Myrddyn Phillips (May 2017)







Mapping Mountains - Significant Height Revisions - Y Trichant

Penmaen Mawr (SH 704 752) - 5th significant height revision

Survey post for Penmaen Mawr

1st Hill Reclassifications post for Penmaen Mawr

2nd Hill Reclassifications post for Penmaen Mawr


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 that was conducted on the 14th July 2016 to a hill that is listed in the Y Trichantwith the hill subsequently analysed with LIDAR data by Aled Williams and it is the latter result that is being detailed in this Significant Height Revisions post.

The criteria for the listing that this height revision affects are:

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  Sub-Trichant - Welsh hills at and above 300m and below 400m in height that have 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming has been published on Mapping Mountains.

The hill is named Penmaen Mawr  and it is situated in the Carneddau range of hills, and is positioned above and to the immediate south of the busy A 55 as it heads westward between the towns of Penmaenmawr and Llanfairfechan, which are situated to the hill’s east and west respectively.


The summit is a part of the hill named Penmaen Mawr and the extended hill has been quarried with its old 1,550ft (472m) map heighted summit now a distant memory as the whole inner section of the summit has been blown apart leaving two remaining tops with this post concentrating on the lower easterly summit.

The lower easterly summit is impressive as it forms a sheer rock face from its south and has steep slopes descending northward to the A 55 below.  Each summit is listed by the same name of Penmaen Mawr as they are both a part of the hill that is known by this name.

The summit area for the whole of Penmaen Mawr now appears on Ordnance Survey maps as a blank area with ‘Quarries’ written over it, and therefore is devoid of any uppermost continuous contour rings, which is the norm for the representation of quarried areas on Ordnance Survey maps, with the highest contour line being 350m for the area where the lower easterly peak is situated.

Therefore this hill’s new summit height is 385.8m (LIDAR data) which is 35.8m higher than its uppermost contour line on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and its 31.3m drop value is sufficient for it to be classified as a Trichant.


The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  385.8m (LIDAR data)

Name:  Penmaen Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 70441 75241

Drop:  31.3m (LIDAR data)



Aled with Penmaen Mawr (SH 704 752) in the background

Myrddyn Phillips (July 2016)






Mapping Mountains - Significant Height Revisions - Y Trichant

Penmaen Mawr (SH 698 755) - 4th significant height revision

Survey post for Penmaen Mawr


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Pedwarau and the Y Trichant, with the survey that resulted in this height revision being conducted on the 14th July 2016.

The criteria for the listings that this height revision affects are:

Y Pedwarau - Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.  300m Double Sub- Pedwarau - Welsh hills at and above 390m and below 400m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.  Sub-Trichant - Welsh hills at and above 300m and below 400m in height that have 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming has been published on Mapping Mountains.

The hill is named Penmaen Mawr  and it is situated in the Carneddau range of hills, and is positioned above and to the immediate south of the busy A 55 as it heads westward between the towns of Penmaenmawr and Llanfairfechan, which are situated to the hill’s east and west respectively.

The summit area of Penmaen Mawr has been quarried, and prior to the first quarry opening in 1830 and the subsequent resulting expansion of operations the hill was substantially higher, with a 1,550ft (472m) map height given it on the Ordnance Survey Popular and New Popular One-Inch maps, with this height also appearing on the Ordnance Survey Six-Inch map published in 1888.

The quarrying of this hill has created two summits with a gaping hole between, the westerly summit is higher than the easterly, although the latter is more impressive due to a shear rock face leading toward its high point.  Each summit is listed by the same name of Penmaen Mawr as they are both a part of the hill that is known by this name, and their height data is given below:

Penmaen Mawr:  390.4m (converted to OSGM15, Trimble GeoXH 6000) at SH 69865 75523

Penmaen Mawr:  385.8m (LIDAR data) at SH 70292 75649

Over recent years the summit area of this hill has appeared without any uppermost contour lines as is the norm for quarried ground that is represented on Ordnance Survey maps, with the highest contour being 370m which appears on the upper western part of this hill.

Therefore this hill’s new summit height is 390.4m (converted to OSGM15) which is 20.4m higher than its uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.


The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  390.4m (converted to OSGM15)

Name:  Penmaen Mawr

OS 1:50,000 map:  115

Summit Grid Reference:  SH 69865 75523

Drop:  26.9m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data 0.39m above the summit of Penmaen Mawr (SH 698 755) which resulted in this hill's significant height revision



Myrddyn Phillips (July 2016)






Mapping Mountains - Significant Height Revisions - Y Trichant

Cefn Llwydallt (SO 074 409) - 3rd significant height revision

Survey post for Cefn Llwydallt


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Trichant, with the following details being retrospective as the survey that resulted in this height revision was conducted on the 29th September 2015.  The Y Trichant comprises all Welsh hills at and above 300m and below 400m in height that have 30m minimum drop, with the Introduction to this list and its re-naming being published on Mapping Mountains.

The name of the hill is Cefn Llwydallt and it is situated in the south-eastern lands of Mynydd Epynt, and is positioned above the small communities of Erwyd (Erwood) to the north-east, Capel Uchaf (Upper Chapel) to the west and Llaneglwys to the south-west.

Access to the hill is relatively easy as the summit is situated on open access land and there is a minor road to the north-west next to where the bwlch of the hill is positioned.  Alternate routes to the summit can use public footpaths from the north-east, east and south that head toward the open access land, with the summit of the hill positioned amongst small gorse bushes.

The hill was surveyed in the afternoon toward the end of a ridge walk that took in a number of hills from Cefn Clawdd (SO 043 403) heading eastward, and prior to the survey with the Trimble GeoXH 6000 the hill was listed as being 378m high based on the old 1,240ft (378.0m) imperial height given the hill on the Ordnance Survey Six-Inch map.

The survey result for the summit produced by the Trimble GeoXH 6000 is 380.7m (converted to OSGM15).  This is not a dramatic height revision when compared to its old listed height, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

Therefore this hill’s new summit height is 380.7m (converted to OSGM15) which is 2.7m higher than the previously listed height of 378m which was based on the old imperial 1,240ft height taken from the Ordnance Survey Six-Inch map.


The full details for the hill are:

Cardinal Hill:  Clepyn Melyn

Summit Height (New Height):  380.7m (converted to OSGM15)

Name:  Cefn Llwydallt

OS 1:50,000 map:  147, 160

Summit Grid Reference:  SO 07422 40950 

Drop:  41.0m (converted to OSGM15)


Gathering data from the summit of Cefn Llwydallt which resulted in this hill's significant height revision


Myrddyn Phillips (October 2015)






Mapping Mountains - Significant Height Revisions - Y Trichant

Coed y Gaer (SO 004 843) - 2nd significant height revision

Survey post for Coed y Gaer


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of Y Trichant and Y Trechol - The Dominant Hills of Wales, with the following details being retrospective as the survey that resulted in this height revision was conducted on 9th February 2014.  The hill is listed as a Lesser Dominant as well as a Trichant, with the latter being the 300m height band of Twmpau (thirty welsh metre prominences and upward) hills.

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

Y Trichant - these are the Welsh hills at or above 300m and below 400m in height that have a minimum drop of 30m. 

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Coed y Gaer and it is situated in the Pegwn Mawr range of hills to the east of Llanidloes, and the survey was conducted in the company of Mark Trengove on a particularly wet and cold day.  The hill can be accessed from a minor lane to the south of its summit; and it overlooks the A470 and the Afon Hafren (River Severn) which are to its north-west.

The height given the hill on current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps is 362m, with the height resulting from the survey with the Trimble being 359.9m (converted to OSGM15).  This is not a dramatic height revision but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.


The full details for the hill are:


Cardinal Hill:  Pegwn Mawr

Summit Height (New Height):  359.9m (converted to OSGM15)

Name:  Coed y Gaer

OS 1:50,000 map:  136

Summit Grid Reference:  SO 00488 84392
  
Drop:  121.7m (converted to OSGM15)

Dominance:  33.80%


Gathering data with the Trimble GeoXH 6000 from the summit of Coed y Gaer



Myrddyn Phillips (August 2015)






Mapping Mountains - Significant Height Revisions - Y Trichant

Old Radnor Hill (SO 251 587) - 1st significant height revision

Survey post for Old Radnor Hill


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of the Y Trichant, with the following details being retrospective as the survey that resulted in this height revision was conducted on 11th January 2014.

The name of the hill is Old Radnor Hill and it is situated in the southern part of the Fforest Glud range of hills, which is known in English as the Radnor Forest, this range of hills is in the heartland of mid Wales and the survey was conducted on a fine and bright winter’s day.

The hill is listed in the Y Trichant, these are the hills in the 300m height band of the Twmpau  (thirty welsh metre prominences and upward) and it is situated south-east of Maesyfed (New Radnor), with the nearest major road being the A44 which skirts the hill on its northern and eastern side.  The A44 road to the east of this hill comprises a road cutting which would significantly increase this hill’s drop value if the natural bwlch is considered to no longer exist and if the nearest point to it is not taken as that for the drop value of the hill.

The summit height of Old Radnor Hill has been dramatically decreased over time due to it being quarried.  However, prior to the survey with the Trimble GeoXH 6000 its listed height was an estimated c 317m based on the uppermost contour on the Ordnance Survey enlarged mapping hosted on the Geograph website showing part of a 315m contour ring.

This hill's new summit height is 312.6m, which is 4.6m lower than its previously estimated listed height and 2.4m lower than the 315m uppermost ring contour on the Ordnance Survey enlarged mapping on the Geograph website.


The full details for the hill are:


Cardinal Hill:  Gwaun Ceste

Summit Height (New Height):  312.6m (converted to OSGM15)

Name:  Old Radnor Hill

OS 1:50,000 map:  148

Summit Grid Reference:  SO 25135 58770
  
Drop:  89.9m (Trimble summit and LIDAR bwlch)

The quarried remains of Old Radnor Hill



Myrddyn Phillips (August 2015)