Mapping Mountains - Significant Height Revisions - 600m Twmpau
Pt. 631.7m (SH 733 622) - 7th significant height revision
There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.
Pt. 631.7m (SH 733 622) |
600m Twmpau by Myrddyn Phillips |
Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR image of Pt. 631.7m (SH 733 622) |
LIDAR summit image of Pt. 631.7m (SH 733 622) |
The full details for the hill are:
Group: Carnedd Llywelyn
Name: Pt. 631.7m
OS 1:50,000 map: 115
Summit Height (New Height): 631.7m (LIDAR)
Summit Grid Reference: SH 73366 62247 & SH 73365 62246 (LIDAR)
Bwlch Height: 595.9m (LIDAR)
Bwlch Grid Reference: SH 73256 62104 (LIDAR)
Drop: 35.8m (LIDAR)
Myrddyn Phillips (September 2024)
Mapping Mountains - Significant Height Revisions - 600m Twmpau
Cefn Dylif (SJ 089 369) - 6th significant height revision
There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau, The Welsh Highlands – Uchafion Cymru and Y Pellennig – The Remotest Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams with assistance from Mark Trengove.
The criteria for the three listings that this height revision applies to are:
600m Twmpau - Welsh hills at or above 600m and below 700m in height with 30m minimum drop, with an accompanying sub list entitled the 600m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 600m and below 700m in height with 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.
The 600m Twmpau by Myrddyn Phillips |
The Welsh Highlands - Uchafion Cymru by Myrddyn Phillipa and Aled Williams |
Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams |
When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 36m of drop based on the 621m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 585m bwlch height based on interpolation of 10m contouring between 580m – 590m. The drop value for this hill was later amended to an estimated c 38m, based on an estimated c 583m bwlch height based on interpolation of 5m contouring between 580m – 585m that appeared on the OS Maps website.
Extract from the Ordnance Survey 1:25,000 Explorer map |
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.
The Trimble GeoXH 6000 gathering data at the summit of Cefn Dylif |
The full details for the hill are:
Group: Y Berwyn
Name: Cefn Dylif
OS 1:50,000 map: 125
Summit Height (New Height): 618.3m (converted to OSGM15)
Summit Grid Reference: SJ 08943 36942
Bwlch Height: 581.3m (converted to OSGM15)
Bwlch Grid Reference: SJ 09068 36590
Drop: 37.0m
Cnicht (SH 645 466) - 5th significant height revision
Survey post for Cnicht
Cnicht (SH 645 466) |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The Trimble GeoXH 6000 gathering data at the summit of Cnicht |
The full details for the hill are:
Bwlch Height: 585.7m (converted to OSGM15)
Foel Lwyd (SH 720 723) - 4th significant height revision
Survey post for Foel Lwyd
Foel Lwyd (SH 720 723) |
Extract from the Ordnance Survey Vector Map local hosted on the Geograph website and which is entitled the Interactive Coverage Map |
The Leica GS15 set-up position at the summit of Foel Lwyd |
Mapping Mountains - Significant Height Revisions - 600m Twmpau
Pen y Boncyn Trefeilw (SH 962 283) - 3rd significant height revision
Survey post for Pen y Boncyn Trefeilw
Pen y Boncyn Trefeilw (SH 962 283) |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The Trimble GeoXH 6000 gathering data at the summit of Pen y Boncyn Trefeilw |
The above details have now been superseded by the Leica RX1250 survey conducted by Alan Dawson, and it is this summit result that is given below.
Mapping Mountains - Significant Height Revisions - 600m Twmpau
Mynydd yr Hewyrch (SH 816 150) - 2nd significant height revision
Summit survey post for Mynydd yr Hewyrch
Bwlch survey post for Mynydd yr Hewyrch
The criteria for the three listings that this height revision affects are:
Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams.
600 Twmpau - These are the Welsh hills at or above 600m and below 700m in height that have a minimum drop of 30m. The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips.
Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. The list is authored by Myrddyn Phillips.
The name that the hill is currently listed by is Mynydd yr Hewyrch and it is situated in the hills of the Rhwng Dyfi a Dulas range which have been referred to as the Bryniau Dyfi and which are situated in the south-western part of north Wales, with the survey of this hill conducted during the late afternoon in the company of Alan Dawson, who had suggested the walk and also surveyed the hill with his Leica RX1250, and it is the result from the Leica equipment that is being used for this hill's data.
Dominance: 46.87%
The Trimble GeoXH 6000 gathering data at one of the three positions surveyed atop Mynydd yr Hewyrch which when coupled with the Leica RX1250 survey resulted in this hill's significant height revision |
Mapping Mountains - Significant Height Revisions - 600m Twmpau
Crib y Rhiw (SH 663 248) - 1st significant height revision
Summit survey post for Crib y Rhiw
Bwlch survey post for Crib y Rhiw
Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams.
Welsh Highlands - All Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams.
600m Twmpau - All Welsh hills at or above 600m and below 700m in height with 30m minimum drop. With the 600m Sub-Twmpau being all Welsh hills at or above 600m and below 700m in height with 20m or more and below 30m of drop. The word Twmpau is an acronym for thirty welsh metre prominences and upward and the list is authored by Myrddyn Phillips.
Gathering data at the summit of Crib y Rhiw which resulted in the significant height revision of this hill |
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