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

 

Troed Rhiw Bylchau (SN 761 471)

There has been a Significant Height Revision to a hill that used to be 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Troed Rhiw Bylchau (SN 761 471)

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

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

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

The name the hill is listed by is Troed Rhiw Bylchau, and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-east and south-west, and has the town of Llanwrtyd towards the east.

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

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 19m of drop, based on the 383m summit spot height that appears n the Ordnance Survey 1:25,000 Explorer map and the 364m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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. 

LIDAR summit image of Troed Rhiw Bylchau (SN 761 471)

The summit height produced by LIDAR analysis is 387.8m and is positioned at SN 76197 47177, 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 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 387.8m and this was derived from LIDAR analysis, this is 4.8m higher than the previously listed 383m summit height, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Esgair Wen 

Name:  Troed Rhiw Bylchau 

OS 1:50,000 map:  146, 147

Summit Height (New Height):  387.8m (LIDAR)                                                           

Summit Grid Reference:  SN 76197 47177 (LIDAR) 

Bwlch Height:  360.6m (LIDAR) 

Bwlch Grid Reference:  SN 76205 47017 & SN 76217 47008 (LIDAR) 

Drop:  27.1m (LIDAR) 

 

Myrddyn Phillips (April 2026)

 

Monthly Synopsis

 

Synopsis of all major changes detailed on Mapping Mountains during the last calendar month.  These can include new, confirmation and retrospective changes

 

Hill Reclassifications: 

Carreg Rhoson (SM 665 254) - 30-99m Double Sub-Twmpau deletion

Twyni Mawr (SN 606 938) - Welsh P15 addition

 

Significant Height Revisions: 

Grinllwm (SH 772 625) - The Welsh P15s

Coed Penllyn (SH 786 696) - 100m Twmpau

Bryn Berw (SN 714 505) - Y Pedwarau - The 400m Hills of Wales

Summit Relocations: 

Llanfair Hill (SO 255 785) - The Fours - The 400m Hills of England

Disgwylfa (SO 172 841) - The Fours - The 400m Hills of England

Yr Eifl (SH 364 447) - 500m Twmpau, Y Trechol - The Dominant Hills of Wales and The Welsh Highlands - Uchafion Cymru

Significant Name Changes: 

Chwarel Penrhyn (SH 621 658) - 200m Twmpau

Disgwylfa (SO 172 841) - The Fours - The 400m Hills of England

Mapping Mountains – Summit Relocations – 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru

 

Yr Eifl (SH 364 447) 

There has been a Summit Relocation that is retrospective to a hill that is listed in the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop, the dominance and status of the hill derived from a Leica GS15 summit survey conducted by John Barnard, Graham Jackson and Myrddyn Phillips, and LIDAR bwlch analysis conducted by Aled Williams.

Yr Eifl (SH 364 447)

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

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.  The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format. 

500m 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 Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023. 

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Yr Eifl and it is adjoined to its own group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its north-east, the B4417 road to its south and the A499 road to its east, and has the villages of Trefor towards the north north-east and Llithfaen towards the south south-west.

When the listings of the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru were first compiled, this hill was listed with a summit height of 564m, based on the spot height adjoined to a triangulation pillar 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

However, it was not until the survey with the Leica GS15 that the details for this hill could be accurately re-assessed.  Although the trig pillar is positioned on a relatively stable base it is positioned on the top of a substantial ancient cairn which consists of a multitude of individual stones and rocks and as this is considered as not being permanent in nature, it is the highest remaining natural ground on the periphery of the ancient cairn that is taken as both its listed summit height and summit position, and when compared to its originally listed summit position 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 either on Ordnance Survey maps or interactive mapping, 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 the de-twinning of a summit, 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.

 

Gathering data with the Leica GS15 at the listed summit position of Yr Eifl

Therefore, the summit height produced by the Leica GS15 survey is 560.7m and this is positioned at SH 36482 44734.  This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, although this position is relatively close to where the triangulation pillar is situated, it is importantly positioned to the highest remaining natural ground on the periphery of the large ancient cairn.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Yr Eifl

Name:  Yr Eifl

OS 1:50,000 map:  123

Summit Height:  560.7m (converted to OSGM15, Leica GS15)

Summit Grid Reference (New Position):  SH 36482 44734 (Leica GS15)  

Bwlch Height:  129.4m (LIDAR)

Bwlch Grid Reference:  SH 45347 48678 (LIDAR)

Drop:  431.3m (Leica GS15 summit and LIDAR bwlch)

 

Myrddyn Phillips and Aled Williams (March 2026)

Mapping Mountains – Significant Name Changes – The Fours – The 400m Hills of England

Disgwylfa (SO 172 841)

There has been a Significant Name Change to a hill that is listed in 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 Disgwylfa (SO 172 841)

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

The Fours – The 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 hill is adjoined to the Cilfaesty group of hills, which are situated adjoined to the Welsh border, and it is positioned with the B4368 road to its north, and minor roads to its west and east, and has the town of Ceri towards the north north-west.

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 10^th 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 provisionally listed under the name of Bettws Hill Wood, which is a prominent name that appears near its summit on the Ordnance Survey 1:25,000 Explorer map, with an estimated c 15m of drop, based on the 427m summit spot height positioned at SO 17503 84053 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 412m col height, based on interpolation of 10m contouring between 410m – 420m. 

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.  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 the latter map that has prompted the change in the listed name of this hill.

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 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 this map that places the name Disgwylfa adjacent to the summit of this hill. 

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

Therefore, the name this hill is now listed by in The Fours – The 400m Hills of England is Disgwylfa, and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map. 

 

The full details for the hill are:

Group:  Cilfaesty

Name:  Disgwylfa

Previously Listed Name:  Bettws Hill Wood

OS 1:50,000 map:  136

Summit Height:  428.9m (LIDAR)

Summit Grid Reference:  SO 17246 84195 (LIDAR)

Col Height:  410.9m (LIDAR)

Col Grid Reference:  SO 17775 83941 (LIDAR)

Drop:  18.0m (LIDAR)

 

Myrddyn Phillips and Aled Williams (March 2026) 

Mapping Mountains – Significant Height Revisions – Y Pedwarau – The 400m Hills of Wales

 

Bryn Berw (SN 714 505)

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Bryn Berw (SN 714 505)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being included in the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Bryn Berw, and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-east and west, and has the village of Llanddewibrefi towards the north-west.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list with a non-interpolated 430m summit height. 

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 28m of drop, based on the 433m summit spot height and the 405m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  And these are the details the hill was listed by when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

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 Bryn Berw (SN 714 505)

LIDAR analysis gives the highest ground on this hill as 430.7m positioned at SN 71433 50501, 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 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 430.7m and this was derived from LIDAR analysis, this is 2.3m lower than the previously listed summit height, which was based on the 433m spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Esgair Wen 

Name:  Bryn Berw 

OS 1:50,000 map:  146, 147

Summit Height (New Height):  430.7m (LIDAR) 

Summit Grid Reference:  SN 71433 50501 (LIDAR) 

Bwlch Height:  403.3m (LIDAR) 

Bwlch Grid Reference:  SN 71373 50607 (LIDAR) 

Drop:  27.4m (LIDAR)

 

Myrddyn Phillips and Aled Williams (March 2026)