Pt. 112.3m (SH 807 793) – 100m Sub-Twmpau deletion
There has been a deletion from the list of 100m Twmpau, 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 Pt. 112.3m (SH 807 793) |
The criteria for the list that this deletion
applies to are:
100m Twmpau
– Welsh hills at or above
100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m
Sub-Twmpau with the criteria for this sub category being all Welsh hills at or
above 100m and below 200m 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.
100m Twmpau by Myrddyn Phillips |
The hill is being listed by the point (Pt. 112.3m)
notation as an appropriate name for it either through local enquiry and/or
historic research has not been found by the author, and it is adjoined
to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A,
Sub-Region A2), and it is positioned encircled
by minor roads, with the A470 road farther to its west and the A55 road farther
to its south-east, and has the town of Llandudno towards the north-west.
When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included
in the Hills to be surveyed sub list
with a non-interpolated c 120m summit height.
After the sub list was standardised, and
interpolated heights and drop values also included the details for this hill
were re-assessed and it was listed with an estimated c 25m of drop, based on an
estimated c 123m summit height and an estimated c 98m bwlch height, with the
summit height based on interpolation of the uppermost 120m ring contour 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 |
Since the original publication of the Welsh P30
lists on Geoff Crowder’s v-g.me website 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.
One of the mapping resources now available online
is the WalkLakes website which hosts an interactive map originated from the
Ordnance Survey Open Data programme.
This map has many spot heights not on other publicly available maps and for
this hill it has a 112m summit spot height.
Extract from the interactive mapping hosted on the WalkLakes website |
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.
Therefore, the deletion of this hill from 100m
Sub-Twmpau status is due to LIDAR analysis, resulting in a 112.3m summit height
and a 98.6m bwlch height, with these values giving this hill 13.8m of drop,
which is insufficient for it to be classified as a 100m Sub-Twmpau.
The full details for the hill are:
Group: Mynydd Hiraethog
Name: Pt. 112.3m
OS 1:50,000 map: 116
Summit Height: 112.3m (LIDAR)
Summit Grid Reference: SH 80726 79335 (LIDAR)
Bwlch Height: 98.6m (LIDAR)
Bwlch Grid Reference: SH 80692 79102 (LIDAR)
Drop: 13.8m (LIDAR)
Myrddyn Phillips (June
2024)
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