Penymorwydd (SH 384 912)
There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips.
LIDAR image of Penymorwydd (SH 384 912) |
30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum
drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the
criteria for this sub category being all Welsh hills at or above 30m and below
100m 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 30-99m Twmpau by Myrddyn Phillips |
When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the 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 an estimated c 26m of drop based on the 69m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 43m bwlch height based on interpolation of 5m contouring between 40m – 45m.
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Penymorwydd |
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, this hill’s new listed summit height is 70.5m and this was derived from LIDAR analysis, this is 1.5m higher than the previous listed summit height of 69m 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: Ynys Môn
Name: Penymorwydd
OS 1:50,000 map: 114
Summit Height (New Height): 70.5m (LIDAR)
Summit Grid Reference: SH 38471 91255 (LIDAR)
Bwlch Height: c 43m (interpolation)
Bwlch Grid Reference: SH 38636 90826 (interpolation)
Drop: c 28m (LIDAR summit and interpolated bwlch)
Myrddyn Phillips (July
2021)
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