Erw Hir (SJ 102 076)
There has been a Summit Relocation to a hill that
is listed in the 200m 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.
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LIDAR image of Erw Hir (SJ 102 076) |
The criteria for the list that this summit relocation applies to are:
200m Twmpau – Welsh hills at or above 200m and below 300m in height that
have 30m minimum drop, with an accompanying sub list
entitled the 200m Sub-Twmpau, with the criteria for this sub category being all
Welsh hills at or above 200m and below 300m in height with 20m or more and
below 30m of drop. The list is authored by
Myrddyn Phillips, with the word Twmpau being an
acronym standing for thirty welsh metre prominences and upward.
|
200m Twmpau by Myrddyn Phillips |
The name the hill is now listed by is Erw Hir, and
this was derived from the Tithe map, and it is adjoined to the Esgeiriau
Gwynion group of hills, which are situated in the southern
part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north
and east, the A495 road to its north-west and the A458 road to its south, and
has the town of Llanfair Caereinion towards the south.
After the accompanying 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 72m of drop, based
on the 233m summit spot height positioned at SJ 10300 07633 and an estimated c
161m bwlch height, based on interpolation of 5m contouring between 160m - 165m. The drop value of this hill has subsequently
reduced due to a bwlch swap with Cae TÅ· Cefn Ysgubor (SJ 111 080).
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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.
LIDAR analysis gives the highest ground on this
hill as 231.4m positioned at SJ 10294 07618.
However, this is a part of a raised field boundary and protocols dictate
that as this is deemed a relatively recent man-made construct such ground is
discounted from the height of a hill.
|
LIDAR summit image of Erw Hir (SJ 102 076) |
The height produced by LIDAR analysis to the natural
summit of this hill is 231.3m and this is positioned at SJ 10280 07620, and this comes within the parameters of the
Summit Relocations used within this page heading, these parameters are:
The term Summit Relocations applies when the high
point of the hill is found to be positioned; in a different field, to a
different feature such as in a conifer plantation, within a different map contour either on Ordnance
Survey maps or interactive mapping, to a different point where a number of
potential summit positions are within close proximity, when natural ground or
the natural and intact summit of a hill is confirmed compared to a higher point
such as a raised field boundary or covered reservoir that is considered a
relatively recent man-made construct, or a relocation of approximately 100
metres or more in distance from either the position of a map spot height or
from where the summit of the hill was previously thought to exist.
Therefore, the summit
height produced by LIDAR analysis is 231.3m and this is positioned at SJ 10280
07620, this position is relatively close to where the spot height appears on
the Ordnance Survey 1:25,000 Explorer map, and is approximately 14 metres westward from the high point of the raised
field boundary.
The full details for the
hill are:
Group: Esgeiriau Gwynion
Name: Erw Hir
OS 1:50,000 map: 125
Summit Height: 231.3m (LIDAR)
Summit Grid Reference
(New Position): SJ 10280 07620 (LIDAR)
Bwlch Height: 197.0m (LIDAR)
Bwlch Grid
Reference: SJ 10681 08135 (LIDAR)
Drop: 34.3m (LIDAR)
Myrddyn Phillips
(January 2025)