Mapping Mountains - Significant Height Revisions - 500m Twmpau
Blorens (SO 269 118) - 6th significant height revision
There has been a Significant Height Revision to a hill that is listed in the 500m 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 a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Aled Williams and Myrddyn Phillips.
Blorens (SO 269 118) |
The 500m Twmpau by Myrddyn Phillips |
Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The Trimble GeoXH 6000 gathering data at the summit of Blorens |
The full details for the hill are:
Group: Cefn yr Ystrad
Name: Blorens
OS 1:50,000 map: 161
Summit Height (New Height): 558.9m (converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference: SO 26974 11830 (Trimble GeoXH 6000)
Bwlch Height: 426.9m (LIDAR)
Bwlch Grid Reference: SO 21949 10939 (LIDAR)
Drop: 132.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)
Aled Williams and Myrddyn Phillips (March 2023)
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Twyn Crug yr Afan (SS 920 954) - 5th significant height revision
Survey post for Twyn Crug yr Afan
There has been a Significant Height Revision to a hill that is listed in the 500m 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 a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams.
Twyn Crug yr Afan (SS 920 954) |
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.
The 500m Twmpau by Myrddyn Phillips |
The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams |
Extract from the Ordnance Survey 1:50,000 Landranger map |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were reassessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available maps and for this hill it had a 559m summit spot height adjoined to the ancient tumulus and positioned at SS 92037 95445.
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 also has many spot heights not on other publicly available Ordnance Survey maps and for this hill the 559m summit spot height is also shown.
Extract from the Magic Maps website |
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.
The Trimble GeoXH 6000 gathering data at the summit of Twyn Crug yr Afan |
The full details for the hill are:
Group: Cymoedd Morgannwg
Name: Twyn Crug yr Afan
OS 1:50,000 map: 170
Summit Height (New Height): 560.2m (converted to OSGM15)
Summit Grid Reference: SS 92035 95448
Bwlch Height: 526.0m (converted to OSGM15)
Bwlch Grid Reference: SS 92019 95054
Drop: 34.2m
Carreg Croes Ifor (SO 248 106) - 4th significant height revision
Summit Relocations post for Carreg Croes Ifor
LIDAR image of Carreg Croes Ifor (SO 248 106) |
Extract from the Ordnance Survey 1:25,000 Explorer map |
Extract from the Ordnance Survey 1:25,000 Historical map |
Extract from the Ordnance Survey series of Six-Inch maps |
LIDAR summit image for Carreg Croes Ifor |
Banc y Foel (SN 725 186) - 3rd significant height revision
Survey post for Banc y Foel
Significant Name Changes post for Banc y Foel
Banc y Foel (SN 725 186) |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The Trimble GeoXH 6000 gathering data at the summit of Banc y Foel (SN 725 186) which resulted in this hill's significant height revision |
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Mynydd Ton (SS 949 940) - 2nd significant height revision
2nd survey post for Mynydd Ton
1st survey post for Mynydd Ton
Summit Relocations post for Mynydd Ton
There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to a hill listed in the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with the survey that resulted in this height revision being conducted on the 23rd July 2016.
The criteria for the 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
500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop. The list is authored by Myrddyn Phillips.
The name of the hill is Mynydd Ton and it is situated in the Y Cymoedd range of hills in south Wales, and the survey was conducted on a warm and sunny afternoon in good, clear conditions. The Y Cymoedd are an extensive group of hills and comprise the area of the south Wales valleys.
The Trimble GeoXH 6000 gathering data beside the ancient cairn at the old summit position of Mynydd Ton which resulted in this hill's significant height revision |
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Twyn Walter (SN 828 175) - 1st significant height revision
Survey post for Twyn Walter
Hill Reclassifications post for Twyn Walter
There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to the listing of the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 10th July 2014.
The criteria for these listings appear below:
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
500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop. With the 500m Sub-Twmpau being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop. The list is authored by Myrddyn Phillips.
Therefore this hill’s new summit height is 6.9m lower than its previously listed height which came from the 509m spot height on current Ordnance Survey 1:25,000 Explorer maps and the Ordnance Survey enlarged mapping hosted on the Geograph website.
Since this height revision was announced the height and position of this hill's bwlch has been determined via LIDAR analysis conducted by Aled Williams, the details for which are given below.
Summit Height (New Height): 502.1m (converted to OSGM15)
Bwlch Grid Reference: SN 82597 17917 (LIDAR)
Gathering data from the summit of Twyn Walter which resulted in this hill's significant height revision |
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