Myrddyn Phillips - Mapping Mountains: Plas Cemlyn

Showing posts with label Plas Cemlyn. Show all posts

Thursday, 24 June 2021

Mapping Mountains – Significant Name Changes – The Welsh P15s

Plas Cemlyn (SH 327 936)

There has been a Significant Name Change to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Plas Cemlyn (SH 327 936)

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

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop. The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019.

The Welsh P15s by Myrddyn Phillips

The hill is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned almost entirely surrounded by the coast with minor roads to its south and south-east, and has the village of Cemaes towards the east.

When the listing that became known as The Welsh P15s was being compiled, this hill was listed under the point (Pt. 18m) notation with an estimated c 15m of drop, based on the 18m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, with this spot height now appearing on the interactive mapping on the Magic Maps website and an estimated c 3m bwlch height based on interpolation of 5m contouring between 0 – 5m.

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

As the summit of this hill comprises bounded land the details for it were examined on the Tithe map. The term Tithe map is generally given to a map of a Welsh or English parish or township and which was prepared after the 1836 Tithe Commutation Act. This act allowed tithes to be paid in cash rather than goods. The Tithe maps gave names of owners and occupiers of land in each parish and importantly for place-name research they also included the name of enclosed land. This enclosed land is usually based on a field system, however not every field is given a name, but many are and especially so in Wales.

Extract from the Tithe map

The enclosed land where the summit of this hill is situated is given the number 2 on the Tithe map, this can be cross referenced against the apportionments; it is these apportionments that give the name of the owner or occupier of the land as well as the name of the land. The land where the summit of this hill is situated is named as Plas Cemlyn in the apportionments, with the details on the Tithe map appearing in the parish of Llanrhwydrys and in the county named as Anglesey.

Extract from the apportionments

Therefore, the name this hill is now listed by in The Welsh P15s is Plas Cemlyn and this was derived from the Tithe map.

The full details for the hill are:

Group: Ynys Môn

Name: Plas Cemlyn

Previously Listed Name: Pt. 18m

OS 1:50,000 map: 114

Summit Height: 20.3m (LIDAR)

Summit Grid Reference: SH 32729 93641 (LIDAR)

Bwlch Height: 2.3m (LIDAR)

Bwlch Grid Reference: SH 32454 93517 (LIDAR)

Drop: 18.0m (LIDAR)

Myrddyn Phillips (June 2021)

Tuesday, 22 June 2021

Mapping Mountains – Significant Height Revisions – The Welsh P15s

Plas Cemlyn (SH 327 936)

There has been a Significant Height Revision to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Plas Cemlyn (SH 327 936)

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

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Plas Cemlyn and this was derived from the Tithe map and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned almost entirely surrounded by the coast with minor roads to its south and south-east, and has the village of Cemaes towards the east.

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

When the listing that became known as The Welsh P15s was being compiled, this hill was listed with an estimated c 15m of drop, based on the 18m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, with this spot height now appearing on the interactive mapping on the Magic Maps website and an estimated c 3m bwlch height based on interpolation of 5m contouring between 0 – 5m.

Extract from the Magic Maps website

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.

The summit height produced by LIDAR analysis is 20.3m 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.

LIDAR summit image of Plas Cemlyn

Therefore, this hill’s new listed summit height is 20.3m and this was derived from LIDAR analysis, this is 2.3m higher than the previous listed summit height of 18m which was based on the summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.