Mapping Mountains – Hill Reclassifications – Y Pedwarau - The 400m Hills of Wales

Mynydd Ty’n y Fach (SH 687 097) – 400m Sub-Pedwar deletion

There has been a deletion from the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Mynydd Ty'n y Fach (SH 687 097)

The criteria for the list that this deletion applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being deleted from the 400m Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format. 

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Ty’n y Fach, and it is adjoined to the Cadair Idris range of hills, which are situated in the south-western part of North Wales (Region C1, Sub-Region C1B), and it is positioned between the stream valleys of the Afon Cadair to its west and the Afon Dysynni to its south-east, and has the small community of Abergynolwyn towards the south south-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

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

After the 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 20m of drop, based on the 409m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 389m bwlch height, based on interpolation of 10m contouring between 380m – 390m, and these are the details given the hill when the 1^st edition of the Y Pedwarau, now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in May 2013.

LIDAR image of Mynydd Ty'n y Fach (SH 687 097)

However, it was not until LIDAR became available and the subsequent survey with the Trimble GeoXH 6000 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.

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Ty'n y Fach

Therefore, the deletion of this hill from 400m Sub-Pedwar status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in a 408.4m summit height and a 389.5m bwlch height, with these values giving this hill 18.9m of drop, which is insufficient for it to be classified as a 400m Sub-Pedwar.

The full details for the hill are:

Group:  Cadair Idris 

Name:  Mynydd Ty’n y Fach

OS 1:50,000 map:  124

Summit Height:  408.4m (converted to OSGM15)

Summit Grid Reference:  SH 68787 09703

Bwlch Height:  389.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 69047 09685

Drop:  18.9m

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (May 2018)