Bryn Gwyn (SJ 213 617)
There has been a Significant Height Revision to a
hill that is listed in the Y Trichant –
The 300m Hills of Wales, with the summit height and its position confirmed
by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and which took
place on the 18th December 2019.
 |
| Gathering data at the the summit of Bryn Gwyn (SJ 213 617) |
The criteria for the list this height revision affects are:
Y Trichant
– The 300m Hills of Wales – Welsh
hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the
Sub-Trichant with the criteria for
this sub category being all Welsh hills at or above 300m and below 400m in
height with 20m or more and below 30m of drop.
The list is authored by
Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13th May 2017.
The name the hill is listed by is Bryn Gwyn and it
is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of
North Wales (Region A, Sub-Region A2), and
it is positioned with the A494 road to its north and minor roads to its west,
south and east, and has the village of Gwernymynydd towards the north.
When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of
this hill was listed as c 335m which was based on a non-interpolated height of
its uppermost contour that appears on Ordnance Survey 1:25,000 Explorer maps.
 |
| Extract from the Ordnance Survey 1:25,000 Explorer map |
After the P30 lists were standardised, and
interpolated heights and drop values also included the details for this hill
were re-evaluated when the Ordnance Survey Vector Map Local hosted on the
Geograph website and which is entitled the Interactive Coverage Map became
available online. This mapping had many
spot heights not on other publicly available Ordnance Survey maps and gave a
339m summit height for this hill. The
339m summit spot height also appears on Ordnance Survey data available on the
Magic Maps website.
 |
| Extract from the Magic Maps website |
The summit height produced by the Trimble GeoXH
6000 is 338.6m and is positioned at SJ 21352 61727, this is not a dramatic
height revision when compared to some revised heights, but it does come 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.
Therefore, this hill’s new listed summit height is
338.6m and this was derived from a Trimble GeoXH 6000 survey, this is 3.6m
higher than the non-interpolated c 335m summit height that was previously given
for this hill.
The full details for the hill are:
Group: Moel y Gamelin
Name: Bryn Gwyn
OS 1:50,000 map: 117
Summit Height (New Height):
338.6m (converted to OSGM15)
Summit Grid Reference:
SJ 21352 61727
Bwlch Height: c 302m (interpolation)
Bwlch Grid Reference:
SJ 21258 61471 (interpolation)
Drop: c 37m (Trimble
GeoXH 6000 summit and interpolated bwlch)
Myrddyn Phillips (April 2020)
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