Mapping Mountains – Significant Name Changes – Y Pedwarau - The 400m Hills of Wales

Pen Twyn (SN 857 463)

There has been a Significant Name Change to a hill that is listed in the Y Pedwarau, and the following details are in respect of a hill that was surveyed with the Trimble GeoXH 6000 on the 25^th September 2015.

The criteria for the list that this name change applies to are:

Y Pedwarau - These are the Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams, and the introduction to the Mapping Mountains publication of this list appeared on the 30th January 2017.

The hill is a part of the Elenydd range, which forms one of the largest hill groups in the country and is situated in the central part of mid and west Wales.  The hill is on the south-eastern periphery of this hill range and is positioned above the small town of Llanwrtyd (Llanwrtyd Wells) to its east.

The Trimble GeoXH 6000 gathering data at the summit of Pen Twyn

The hill appeared in the 400m P30 list on Geoff Crowder’s v-g.me website under the name of Pen Garn-gou, which is a name that appeared close to the summit of the hill on Ordnance Survey 1:25,000 Explorer maps of the day.  During my early hill listing I paid little regard to name placement on a map, or the meaning of names and to what feature the name was appropriately applied to.  Therefore I prioritised names for listing purposes that I now understand are inappropriate, and Pen Garn-gou is such an example as this name has been consistently applied by the Ordnance Survey to land that is below and to the south of this hill’s summit, whilst the larger scale Ordnance Survey Six-Inch map is consistent in applying the name Pen Twyn to the land where the summit of the hill is situated.   

Pen Garn-gou

477m

SN858463

147

187

  

Since publication of these P30 lists on Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historical such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the enlarged map on the Geograph website.  One of the historical maps now available is the Ordnance Survey One-Inch ‘Old Series’ map which was the first map made publicly available by the Ordnance Survey, and it is details on this map that formed the basis for the change in this hill’s listed name. 

Extract from the Ordnance Survey One-Inch 'Old Series' map

Extract from the series of Ordnance Survey Six-Inch maps

The One-Inch ‘Old Series’ was the first map that Ordnance Survey published, and these maps were based on the preceding Draft Surveyors map.  Their publication culminated from the whole of Britain being surveyed between 1791 and 1874 and the detail gathered therein produced at a scale of one inch to the mile and published in sheet format between 1805 and 1874.  The One-Inch ‘Old Series’ maps for the whole of Wales are now available online; they are also available in map format as enlarged and re-projected versions to match the scale and dimensions of the Ordnance Survey 1:50,000 Landranger series and are published by Cassini.  This series of maps forms another important part in the study of Welsh upland place-names and bridge the time frame leading to the production of the Ordnance Survey base map of the Six-Inch series.

Therefore the name this hill is now listed by in Y Pedwarau is Pen Twyn and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map and later confirmed by the series of Ordnance Survey Six-Inch maps.

The full details for the hill are:

Group:  Elenydd

Name:  Pen Twyn

Previously Listed Name:  Pen Garn-gou

 

Summit Height:  476.6m (converted to OSGM15)

OS 1:50,000 map:  147

Summit Grid Reference:  SN 85798 46301

  

Drop:  45.1m (Trimble summit and LIDAR bwlch)

For details on the survey of Pen Twyn

Myrddyn Phillips and Aled Williams (September 2016)