Thursday, 16 July 2026

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

 

Gaer Fawr (SJ 223 129) 

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 a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips.                       

Gaer Fawr (SJ 223 129)

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 3rd 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 Carnedd Wen group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A2), and it is positioned with minor roads to its north and west, and the B4392 road to its south-east, and has the village of Cegidfa (Guilsfield) towards the south. 

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

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill appeared under the transposed name of Gaer-fawr Hill, which is a prominent name that appears adjacent to the summit of this hill on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.


Gaer-fawr Hill219mSJ224130126240


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 instance transpose a prominent name that appears adjacent to the hill on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.  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.

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.  Two of the historic maps now available online are the Ordnance Survey Draft Surveyors map which formed the basis for the first publicly available Ordnance Survey One-Inch ‘Old Series’ map, and it is these maps along with local enquiry that prompt the change in the listed name of this hill.

The Draft Surveyors maps consist of the preliminary drawings made by the Ordnance Survey surveyors between the 1780s and 1840 and formed the basis for the first publicly available One-Inch map.  They were drawn at scales of six inches to the mile for areas considered of particular military significance and down to two inches to the mile for other areas.  Fair copies were then produced from these preliminary drawings to one inch to the mile and then copper plates were prepared for printing.  The Draft Surveyors maps for the whole of Wales are now available online and they form an important part in the study of Welsh upland place-names as they bridge the time frame between the late 18th century and the mid-19th century when the Ordnance Survey produced their first One-Inch maps, and importantly for this hill and its listed name, it is this map that records the name Gaer Fawr adjacent to the summit of this hill. 

Extract from the Ordnance Survey Draft Surveyors Map

The One-Inch ‘Old Series’ map was the first map that Ordnance Survey produced, and their publication culminated from the whole of Britain being surveyed between 1791 and 1874 and the detail gathered therein produced at a scale of one inch to the mile and published in sheet format between 1805 and 1874.  The One-Inch ‘Old Series’ maps for the whole of Wales are now available online; they are also available in map format as enlarged and re-projected versions to match the scale and dimensions of the Ordnance Survey 1:50,000 Landranger series and are published by Cassini.  This series of maps form another important part in the study of Welsh upland place-names and bridge the timeframe leading up to the production of the Ordnance Survey base map of the Six-Inch series, and importantly for this hill and its listed name, it is also this map that places the name Gaer Fawr adjacent to the summit of this hill. 

Extract from the Ordnance Survey One-Inch 'Old Series' map

The intricacies of language and prioritising one in favour of another for listing a hill is fraught with complication, with originating Cymraeg names being anglicised and also originating English names being cymricised, examples such as these are more common in border country and especially so for anglicised forms.  There is no steadfast rule that fits all, but as a standard a name that has its origins in the Welsh language and where this is substantiated by either historic documentation and/or contemporary usage should be prioritised in favour of a contemporary anglicised or English version of the name.  Likewise, if a name exists where an element of it is in English and if this name applies to a hill that is situated in a Welsh speaking part of Wales it is standard practice to use a full Welsh term for the name.  It is also standard practice to use a Welsh name for a hill if another name exists that has originated in a different language.

Therefore, the name this hill is now listed by in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales is Gaer Fawr and this was derived from a variety of sources including the Ordnance Survey Draft Surveyors Map and the Ordnance Survey One-Inch ‘Old Series’ map.  The Hill part of this name that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map is a later addition, with local pronunciation favouring the exclusion of this word with the use of Gaefer being predominant. 

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Gaer Fawr 

Previously Listed Name:  Gaer Fawr Hill   

OS 1:50,000 map:  126

Summit Height:  217.6m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SJ 22394 12995 (Trimble GeoXH 6000)               

Bwlch Height:  138.7m (LIDAR) 

Bwlch Grid Reference:  SJ 21991 13145 (LIDAR) 

Drop:  78.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  36.26% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (July 2026)

Monday, 13 July 2026

Mapping Mountains – Hill Reclassifications – The Fours – The 400m Hills of England


Almsworthy Common (SS 841 420) – Sub-Four exclusion

There has been an exclusion from the listing of the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Almsworthy Common (SS 841 420)

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

The FoursThe 400m Hills of England - English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Almsworthy Common, and it is adjoined to the Dunkery Beacon group of hills, which are situated in the counties of Somerset and Devon, and it is positioned encircled by minor roads with the the B3223 road and the B3224 road farther to its south, and has the village of Porlock towards the north-east.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop.

Prior to this revision this hill was listed with an estimated c 16m of drop, based on the 453m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 437m col height, based on interpolation of 10m contouring between 430m – 440m. 

Extract from the 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.

Therefore, the exclusion of this hill from Sub-Four status is due to LIDAR analysis, resulting in a 453.8m summit height and a 439.1m col height, with these values giving this hill 14.7m of drop, which is insufficient for it to be classified as a Sub-Four. 

 

The full details for the hill are:

Group:  Dunkery Beacon

Name:  Almsworthy Commom

OS 1:50,000 map:  181

Summit Height:  453.1m (LIDAR)

Summit Grid Reference:  SS 84151 42008 (LIDAR)

Col Height:  439.1m (LIDAR)

Col Grid Reference:  SS 83776 42521 (LIDAR)

Drop:  14.7m (LIDAR)

 

For the additions, deletions and reclassifications to The Fours – The 400m Hills of England reported on Mapping Mountains since the December 2013 publication of the 1st edition of this list by Europeaklist please consult the following Change Registers:

 

The Fours

 

Sub-Fours

 


Myrddyn Phillips and Aled Williams (July 2026)                


Friday, 10 July 2026

Mapping Mountains – Significant Height Revisions – The 500-Metre Tops of England and Wales – Deweys


Rhobell Ganol (SH 785 274) 

There has been a Significant Height Revision to a hill that is listed in the The 500-Metre Tops of England and Wales, 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 Rhobell Ganol (SH 785 274)

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

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop. 

Mountain tables by Michael Dewey

Michael Dewey died on the 5th November 2022.  His wife; Gillian wished for this list to be carried on and made provision for it to be co-authored by Myrddyn Phillips.  Michael will always be the compiler and originator, it’s just that he’s now got a co-author to safeguard and carry this list on.

The name the hill is listed by is Rhobell Ganol and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales, and it is positioned with a minor road to its north, the A470 road to its west and the A494 road to its east, and has the small community of Rhyd-y-main towards the south south-east.

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

When the original list of Deweys appeared in the Mountain tables book published by Constable in 1995, this hill was listed with a non-interpolated summit height of 520+m, based on the uppermost 520m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

Since the original publication of this list 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.

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This mapping has a 522m summit spot height applied to the southerly top that matches the summit position given the hill by LIDAR analysis. 

Extract from the interactive mapping hosted on the Magic Maps website

Another 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 gives a 522m spot height to a northerly top positioned at SH 78603 27533. 

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 Rhobell Ganol (SH 785 274)

LIDAR analysis gives the summit of this hill as 524.8m positioned at SH 78578 27406, and 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, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or other GNSS equipment or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 524.8m and this was derived from LIDAR analysis, this is 4.8m higher than the originally listed summit height of 520+m, which was based on the non-interpolated uppermost 520m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and 2.8m higher than the spot heights that appear on the Magic Maps interactive map and the interactive mapping hosted on the WalkLakes website. 

 

The full details for the hill are:

Group:  Arenig Fawr

Name:  Rhobell Ganol

OS 1:50,000 map:  124

Summit Height (New Height):  524.8m (LIDAR)

Summit Grid Reference:  SH 78578 27406 (LIDAR)  

Bwlch Height:  485.7m (LIDAR)

Bwlch Grid Reference:  SH 78549 26977 (LIDAR)

Drop:  39.1m (LIDAR)

 

Myrddyn Phillips (July 2026)

  

Tuesday, 7 July 2026

Mapping Mountains – Significant Name Changes – The Welsh P15s

 

Mynydd Deulyn (SH 754 605) 

There has been a Significant Name Change 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 Mynydd Deulyn (SH 754 605)

The criteria for the list that this name change 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 10th May 2019. 

The Welsh P15s by Myrddyn Phillips

The hill is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned between Llyn Crafnant to its north-west and Llyn Geirionydd to its east, with the A5 road to its south, and the B5106 road, the Afon Conwy and the A470 road to its east, and has the village of Capel Curig towards the south-west and the town of Llanrwst towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was listed under the point (Pt. 336m) notation, with an estimated c 14m of drop, based on the 336m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 322m bwlch height, based on interpolation of 10m contouring between 320m – 330m. 

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

Since the original compilation of this list 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 Mynydd Deulyn 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 The Welsh P15s is Mynydd Deulyn, and this was derived from the Ordnance Survey series of Six-Inch maps. 

 

The full details for the hill are: 

Group:  Carnedd Llywelyn 

Name:  Mynydd Deulyn 

Previously Listed Name:  Pt. 336m 

OS 1:50,000 map:  115

Summit Height:  334.8m (LIDAR)                                                           

Summit Grid Reference:  SH 75464 60544 (LIDAR)                                                  

Bwlch Height:  318.4m (LIDAR) 

Bwlch Grid Reference:  SH 75563 60655 (LIDAR) 

Drop:  16.4m (LIDAR) 

 

Myrddyn Phillips (July 2026)