Pt. 690.2m (SH 647 468)
There has been a Significant Height Revision to a
hill that is listed in the Yr Uchafion,
with the summit height, bwlch height and their locations, the drop and status
of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn
Phillips on the 23rd March 2019.
 |
| Pt. 690.2m (SH 647 468) |
The criteria for the listing that this significant
height revision applies to are:
Yr Uchafion – Welsh hills at or above 500m in height that
have 15m minimum drop. The list is
co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4th November 2015.
The hill is currently listed by the point (Pt.
690.2m) notation and it is adjoined to the Moelwynion range of hills, which are
situated in the north-western part of North Wales (Region A, Sub-Region A1),
and it is positioned with the A4085 road to its south-west, the A498 road to
its north-west and the A470 road towards the east, and has the small community
of Croesor towards the south-west and the town of Blaenau Ffestiniog towards
the east.
Prior to the survey with the Trimble GeoXH 6000
this hill was listed with a 688m summit height which appears as a spot height
on the Ordnance Survey Vector Map Local hosted on the Geograph website and
which is entitled the Interactive Coverage Map.
 |
| Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website |
The summit height produced by the Trimble GeoXH
6000 survey is 690.2m, this is not a substantial 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 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 any other GNSS receiver, 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. As
heights on different scaled Ordnance Survey maps are not consistent the height given
on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000
Landranger map for detailing these revisions.
 |
| The Trimble GeoXH 6000 gathering data at the summit of Pt. 690.2m (SH 647 468) |
Therefore, the new summit height of this hill is
690.2m and this was produced by surveying with the Trimble GeoXH 6000, this is 2.2m
higher than its previously listed height of 688m which appears as a spot height
on the Ordnance Survey Vector Map Local hosted on the Geograph website, however
this new height is in accordance with the 5m contouring on OS Maps.
 |
| Extract from the OS Maps website |
The full details for the hill are:
Group: Moelwynion
Name: Pt. 690.2m
OS 1:50,000 map: 115
Summit Height (New height):
690.2m (converted to OSGM15)
Summit Grid Reference:
SH 64799 46864
Bwlch Height: 670.9m
(converted to OSGM15)
Bwlch Grid Reference:
SH 64681 46742
Drop: 19.3m
Myrddyn Phillips and Aled Williams (July 2019)
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