Mapping Mountains – Significant Height Revisions – The Welsh P15s

Llanlleiana Park (SH 386 946) 

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 derived from detail on contemporary maps produced from Ordnance Survey data. 

The criteria for the list that this height revision 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 name the hill is listed by is Llanlleiana Park 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 with the coast to its north, a minor road and the A5025 road farther to its south, and has the village of Cemaes towards the south-west. 

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main P15 list with an estimated c 16m of drop, based on the 44m 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 and an estimated c 28m bwlch height based on interpolation of 5m contouring between 25m – 30m that appear on the Ordnance Survey 1:25,000 Explorer map. 

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

The details for this hill have subsequently been re-assessed against the current Ordnance Survey interactive map hosted on the Geograph website which gives a 46m summit spot height, and current 5m contouring at the bwlch which is between 30m – 35m and estimated as c 32m, with these values giving this hill an estimated c 14m of drop, 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. 

Extract from the Ordnance Survey interactive mapping hosted on the Geograph website

Therefore, this hill’s new listed summit height is 46m and this was derived from the Ordnance Survey interactive map hosted on the Geograph website, this is 2m higher than the previous listed summit height of 44m which appeared as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

 

ills of Wales, and are reproduced below@

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Llanlleiana Park 

OS 1:50,000 map:  114

Summit Height (New Height):  46m (spot height)                                                           

Summit Grid Reference:  SH 38614 94695 (spot height) 

Bwlch Height:  c 32m (interpolation) 

Bwlch Grid Reference:  SH 38606 94628 (interpolation) 

Drop:  c 14m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (July 2021)