Mapping Mountains - Significant Height Revisions - 500m Twmpau
Foel Ganol (SH 687 715) - 9th 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 LIDAR analysis conducted by Aled Williams.
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LIDAR image of Foel Ganol (SH 687 715) |
The criteria for the two listings that this height revision applies to are:
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500m Twmpau by Myrddyn Phillips |
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Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips |
The name the hill is listed by is Foel Ganol and it 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 with the A55 road to its north-west and a minor road to its west, and has the town of Llanfairfechan towards the north.
When the list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 40m of drop, based on the 536m summit spot height and the 496m bwlch spot height that appear on the Ordnance Survey 1:25,000 Explorer map.
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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.
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LIDAR summit image of Foel Ganol (SH 687 715) |
LIDAR analysis gives the summit of this hill as 533.1m positioned at SH 68797 71588, and when compared to its originally listed summit height of 536m 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 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.
Therefore, the new listed summit height of this hill is 533.1m and this was derived from LIDAR analysis, this is 2.9m lower than the originally listed summit height of 536m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.
The full details for the hill are:
Group: Carnedd Llywelyn
Name: Foel Ganol
OS 1:50,000 map: 115
Summit Height (New Height): 533.1m (LIDAR)
Summit Grid Reference: SH 68797 71588 (LIDAR)
Bwlch Height: 495.0m (LIDAR)
Bwlch Grid Reference: SH 69012 71563 (LIDAR)
Drop: 38.2m (LIDAR)
Myrddyn Phillips (September 2024)
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Tryfan (SH 596 580) - 8th significant height revision
Survey post for Tryfan
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.
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Tryfan (SH 596 580) |
The criteria for the two listings that this height revision applies to are:
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500m Twmpau by Myrddyn Phillips |
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Welsh Highlnads - Uchafion Cymru by Aled Williams and Myrddyn Phillips |
The name the hill is listed by is Tryfan and it is adjoined to the Yr Wyddfa group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4086 road to its north-east, and has the village of Llanberis towards the north-west.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
A basic levelling survey conducted by Myrddyn Phillips on the 25.06.04 gave this hill 67ft (20.4m) of drop and therefore it was included in the listing that later became known as the Welsh Highlands – Uchafion Cymru. However, this drop value was at odds with detail on the contemporary Ordnance Survey 1:25,000 Explorer map which has an uppermost 560m summit contour and bwlch contouring between 550m – 560m, with interpolation giving an estimated c 555m bwlch height.
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Extract from the interactive mapping hosted on the WalkLakes website |
The drop value ascertained fron the basic levelling survey implied that current Ordnance Survey contouring on the 1:50,000 Landranger and 1:25,000 Explorer map is missing an uppermost 570m ring contour, and this is evidenced by the 577m summit spot height on the mapping hosted on the WalkLakes website. This website hosts an interactive map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available maps.
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The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 596 580) |
The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 on the 09.09.14, resulting in a 577.2m summit height positioned at SH 59636 58098, and this height 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 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.
Therefore, the new listed summit height of this hill is 577.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 59636 58098 and is 17.2m higher than the uppermost 560m contour that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.
The full details for the hill are:
Group: Yr Wyddfa
Name: Tryfan
OS 1:50,000 map: 115
Summit Height (New Height): 577.2m (converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference: SH 59636 58098 (Trimble GeoXH 6000)
Bwlch Height: 556.4m (converted to OSGM15, Trimble GeoXH 6000)
Bwlch Grid Reference: SH 59683 57996 (Trimble GeoXH 6000)
Drop: 20.8m (Trimble GeoXH 6000)
Myrddyn Phillips (August 2024)
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Tryfan (SH 597 578) - 7th significant height revision
Survey post for Tryfan
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.
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Tryfan (SH 597 578) |
The criteria for the two listings that this height revision applies to are:
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500m Twmpau by Myrddyn Phillips |
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Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips |
The name the hill is listed by is Tryfan and it is adjoined to the Yr Wyddfa group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4086 road to its north-east, and has the village of Llanberis towards the north-west.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
A basic levelling survey conducted by Myrddyn Phillips on the 25.06.04 gave this hill 79½ft (24.2m) of drop and therefore it was included in the listing that later became known as the Welsh Highlands – Uchafion Cymru. However, this drop value was at odds with detail on the contemporary Ordnance Survey 1:25,000 Explorer map which has an uppermost 580m summit contour and bwlch contouring between 560m – 570m, with interpolation giving an estimated c 568m bwlch height.
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Extract from the interactive mapping hosted on the WalkLakes website |
The drop value ascertained fron the basic levelling survey implied that current Ordnance Survey contouring on the 1:50,000 Landranger and 1:25,000 Explorer map is missing an uppermost 590m ring contour, and this is evidenced by the 594m summit spot height on the mapping hosted on the WalkLakes website. This website hosts an interactive map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available maps.
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The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 597 578) |
The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 on the 09.09.14, resulting in a 594.4m summit height positioned at SH 59763 57873, and this height 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 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.
Therefore, the new listed summit height of this hill is 594.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 59763 57873 and is 14.4m higher than the uppermost 590m contour that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.
The full details for the hill are:
Group: Yr Wyddfa
Name: Tryfan
OS 1:50,000 map: 115
Summit Height (New Height): 594.4m (converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference: SH 59763 57873 (Trimble GeoXH 6000)
Bwlch Height: 569.9m (converted to OSGM15, Trimble GeoXH 6000)
Bwlch Grid Reference: SH 59858 57775 (Trimble GeoXH 6000)
Drop: 24.6m (Trimble GeoXH 6000)
Myrddyn Phillips (August 2024)
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Blorens (SO 269 118) - 6th significant height revision
Survey post for Blorens
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.
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Blorens (SO 269 118) |
The criteria for the two listings that this height revision applies to are:
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The 500m Twmpau by Myrddyn Phillips |
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Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams |
The name the hill is listed by is Blorens and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A465 road to its north-east, the B4246 road to its north-west and a minor road to its south, and has the town of Y Fenni (Abergavenny) towards the north-east.
When the list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 133m of drop, based on the 561m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 428m bwlch height, based on interpolation of 10m contouring between 420m – 430m.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 558.9m summit height positioned at SO 26974 11830, and this height 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 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.
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The Trimble GeoXH 6000 gathering data at the summit of Blorens |
Therefore, the new listed summit height of this hill is 558.9m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 26974 11830 and is 2.1m lower than its originally listed height of 561m, which was based on the summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.
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)
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.
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Twyn Crug yr Afan (SS 920 954) |
The criteria for the two listings that this height revision 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.
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The 500m Twmpau by Myrddyn Phillips |
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The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams |
The name the hill is listed by is Twyn Crug yr Afan and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it is positioned with the A4058 road to its north-east and the A4107 road to its immediate south, and has the connecting villages of Blaengwynfi and Abergwynfi towards the west north-west.
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Extract from the Ordnance Survey 1:50,000 Landranger map |
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 31m of drop, based on the 558m spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 527m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
Since the original compilation of this list there have been a number of Ordnance Survey 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 are current and digitally updated such as the old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and the mapping on the OS Maps, Magic Maps and WalkLakes websites.
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.
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Extract from the Magic Maps website |
The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 560.2m positioned at SS 92035 95448 and this height 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 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.
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The Trimble GeoXH 6000 gathering data at the summit of Twyn Crug yr Afan |
Therefore, this hill’s new listed summit height is 560.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SS 92035 95448 and is 2.2m higher than its originally listed height of 558m which appears as a spot height on contemporary Ordnance Survey 1:50,000 Landranger maps, and 1.2m higher than the 559m 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 which now appears on the interactive mapping on the Magic Maps website.
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
Myrddyn Phillips (August 2021)
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 confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 summit survey conducted by Aled Williams.
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LIDAR image of Carreg Croes Ifor (SO 248 106) |
The criteria for the two listings that this height revision 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.
The name the hill is listed by is Carreg Croes Ifor and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road to its north, the B4248 road to its south-west and the B4246 road to its east, and has the town of Blaenafon towards the south south-east.
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 18m of drop based on a non-interpolated c 500m summit height and a 482m bwlch height taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.
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Extract from the Ordnance Survey 1:25,000 Explorer map |
Since first compilation of the Welsh 500m P15 list there are a number of maps now available online, and the details for this hill were re-assessed when the Ordnance Survey 1:25,000 Historical map became available online, and this map gives a 1657ft (505.1m) summit spot height for this hill.
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Extract from the Ordnance Survey 1:25,000 Historical map |
The imperial height on the Ordnance Survey 1:25,000 Historical map is derived from a 1657.4m (505.2m) Surface Height that appears on the Ordnance Survey series of Six-Inch maps. Therefore, the summit height for this hill was revised and listed as 505m with the caveat that since this height was derived this hill has undergone mining activity which has substantially altered the landscape.
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Extract from the Ordnance Survey series of Six-Inch maps |
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.
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LIDAR summit image for Carreg Croes Ifor |
The summit height and position produced by LIDAR analysis is 509.8m at SO 24848 10663, this is a dramatic height revision when compared to some revised heights, and it 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 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.
During analysis of this hill, Aled used overlays from old maps with contemporary maps and the details produced via LIDAR. This shows that the natural 505.2m summit positioned at SO 24810 10620 is now under a substantial amount of mine spoil and this has raised the height of the summit.
The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and as the natural summit is now under a spoil tip and an on-site visit confirms this artificially raised summit to be solid and stable, it is the Trimble summit height and position that is being prioritised for this hill.
Therefore, the new listed summit height of this hill is 509.7m and this was derived from a Trimble GeoXH 6000 survey, this is 4.7m higher than the 505m summit height that was previously given for this hill.
The full details for the hill are:
Group: Cymoedd Gwent
Name: Carreg Croes Ifor
OS 1:50,000 map: 161
Summit Height (New Height): 509.7m (converted to OSGM15, Trimble GeoXH 6000, artificially raised)
Summit Grid Reference: SO 24848 10663 (Trimble GeoXH 6000)
Bwlch Height: 482.1m (LIDAR)
Bwlch Grid Reference: SO 25485 10565 (LIDAR)
Drop: 27.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)
Myrddyn Phillips (May 2020)
Mapping Mountains - Significant Height Revisions - 500m Twmpau
Banc y Foel (SN 725 186) - 3rd significant height revision
Survey post for Banc y Foel
Significant Name Changes post for Banc y Foel
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