Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Glog (SJ 114 037) 

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, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Glog (SJ 114 037)

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 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Glog and this was derived from local enquiry, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it has the B4385 road to its north, the B4389 road to its west, the B4390 road to its south and the B4385 road to its east, and has the small town of Llanfair Caereinion towards the north north-west. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of c 320m, based on the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The summit of this hill has now been surveyed with the Trimble GeoXH 6000 resulting in 315.4m at SJ 11434 03700, this is not a dramatic decrease in height 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. 

The Trimble GeoXH 6000 gathering data at the summit of Glog

Therefore, this hill’s new listed summit height is 315.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SJ 11434 03700 and is 4.6m lower than its previously listed height of c 320m which was based on the uppermost 320m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Carnedd Wen 

Name:  Glog 

OS 1:50,000 map:  136

Summit Height (New Height):  315.4m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SJ 11434 03700 (Trimble GeoXH 6000) 

Bwlch Height:  c 253m (interpolation) 

Bwlch Grid Reference:  SJ 11080 03903 (interpolation) 

Drop:  c 62m (Trimble GeoXH 6000 summit and interpolated bwlch)

 

Myrddyn Phillips (March 2021)