Mapping Mountains – Significant Name Changes – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Coed Garth Gwynion (SN 733 986) 

There has been a Significant Name Change to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Garth Gwynion (SN 733 986)

The criteria for the two listings that this name change applies to are:

200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The hill is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the A487 road to its north-west and a minor road to its east, and has the town of Machynlleth towards the north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list under the transposed name of Mynydd-Garth-Gwynion, which is a prominent name that appears near the summit of this hill on the Ordnance Survey 1:25,000 Explorer map.

Mynydd-Garth-Gwynion

228m

SN733987

135

23

Clem/Yeaman

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day, with little consideration for the meaning of the name and where it was appropriately applied to.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this transpose a name that appears on the Ordnance Survey 1:25,000 Explorer map and use it for that of the hill.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found. 

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, and it is the series of Ordnance Survey Six-Inch maps that form the basis of the change in the listed name of this hill.

The Ordnance Survey series of Six-Inch maps formed the base map Ordnance Survey used for many decades leading to the production of the 1:10,000 Series of maps, both have now been superseded by the digitised Master Map.  The series of Six-Inch maps are excellent for name placement and especially so compared to the contemporary Ordnance Survey 1:25,000 Explorer map, and it is the series of Six-Inch maps that position the name of Coed Garth Gwynion to land where the summit of this hill is situated.

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales is Coed Garth Gwynion, and this was derived from the Ordnance Survey series of Six-Inch maps.  With the previously listed name of Mynydd Garth Gwynion applicable to adjacent enclosed land that does not take in the summit of this hill. 

 

The full details for the hill are:

Group:  Banc Llechwedd Mawr

Name:  Coed Garth Gwynion

Previously Listed Name:  Mynydd-Garyh-Gwynion   

OS 1:50,000 map:  135

Summit Height:  229.7m (LIDAR) 

Summit Grid Reference:  SN 73301 98604 (LIDAR) 

Bwlch Height:  96.7m (LIDAR) 

Bwlch Grid Reference:  SN 73700 98378 (LIDAR) 

Drop:  133.0m (LIDAR) 

Dominance:  57.91% (LIDAR) 

 

Myrddyn Phillips (November 2024)

 

  

Mapping Mountains – Summit Relocations – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

 

Coed Garth Gwynion (SN 733 986) 

There has been confirmation of a Summit Relocation to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Garth Gwynion (SN 733 986)

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

200m Twmpau - Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Coed Garth Gwynion, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the A487 road to its north-west and a minor road to its east, and has the town of Machynlleth towards the north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 228m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 73306 98691. 

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

After 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 with an estimated c 131m of drop, based on the 228m summit spot height and an estimated c 97m bwlch height, based on interpolation of 10m contouring between 90m – 100m.  The summit position was subsequently relocated to match the ten figure grid reference given on the Hill Bagging 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 Coed Garth Gwynion (SN 733 986)

The height produced by LIDAR analysis to the highest ground on this hill is 229.7m and this is positioned at SN 73301 98604, 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, 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 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 229.7m and this is positioned at SN 73301 98604, 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 80 metres southward from the originally listed summit position and importantly it is placed to a different feature; an enclosed field compared to an enclosed wood. 

 

The full details for the hill are: 

Group:  Banc Llechwedd Mawr 

Name:  Coed Garth Gwynion 

OS 1:50,000 map:  135

Summit Height:  229.7m (LIDAR) 

Summit Grid Reference (New Position):  SN 73301 98604 (LIDAR) 

Bwlch Height:  96.7m (LIDAR) 

Bwlch Grid Reference:  SN 73700 98378 (LIDAR) 

Drop:  133.0m (LIDAR) 

Dominance:  57.91% (LIDAR) 

 

Myrddyn Phillips (November 2024)