Myrddyn Phillips - Mapping Mountains: Ynys Cynfelyn

Showing posts with label Ynys Cynfelyn. Show all posts

Sunday, 18 July 2021

Mapping Mountains – Significant Height Revisions – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

Ynys Cynfelyn (SN 649 919)

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Ynys Cynfelyn (SH 649 919)

The criteria for the two listings that this height revision applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The 30-99m Twmpau by Myrddyn Phillips

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Ynys Cynfelyn, and it is adjoined to the Banc Llechwedd Mawr group of hills which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the coast to its west, the B4353 road to its north, a minor road to its south and the A487 road to its east, and has the village of Tal-y-bont towards the south.

When the original 30-99m 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 non interpolated c 40m summit height.

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 36m of drop based on an estimated c 43m summit height and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

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

However, it was not until LIDAR became available 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.

LIDAR summit image of Ynys Cynfelyn (SH 649 919)

The summit height produced by LIDAR analysis is 45.2m and this comes 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 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, the new listed summit height of this hill is 45.2m and this was derived from LIDAR analysis, this is 2.2m higher than the previous listed summit height of c 43m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Group: Banc Llechwedd Mawr

Name: Ynys Cynfelyn

OS 1:50,000 map: 135

Summit Height (New Height): 45.2m (LIDAR)

Summit Grid Reference: SN 64924 91968 (LIDAR)

Bwlch Height: 5.4m (LIDAR)

Bwlch Grid Reference: SN 65436 92025 & SN 65434 92022 (LIDAR)

Drop: 39.8m (LIDAR)

Dominance: 88.05% (LIDAR)

Myrddyn Phillips (July 2021)

Thursday, 8 July 2021

Mapping Mountains – Significant Name Changes – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

Ynys Cynfelyn (SN 649 919)

There has been a Significant Name Change to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Ynys Cynfelyn (SN 649 919)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The 30-99m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height. The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and which is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The hill is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the coast to its west, the B4353 road to its north, a minor road to its south and the A487 road to its east, and has the village of Tal-y-bont towards the south.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was listed under the transposed name of Plas y Gwynfryn, with an accompanying note stating; Name from buildings to the West.

Plas y Gwynfryn

40c

SN649919

135

Name from buildings to the West

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day. My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance transpose the name of a house and use it for that of the hill. This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

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

Online research found reference to this hill is a book entitled Annals and Antiquities of the Counties and County Families of Wales by Thomas Nicholas. The reference in this book names the hill as Ynys Cynfelyn. An extract from this book is given below.

Extract from the Annals and Antiquities of the Counties and County Families of Wales by Thomas Nicholas

Therefore, the name this hill is now listed by in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales is Ynys Cynfelyn and this was derived from the Annals and Antiquities of the Counties and County Families of Wales by Thomas Nicholas.