Mapping Mountains – Summit Relocations – 200m Twmpau

Cae Top (SJ 061 016)

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Cae Top (SJ 061 016)

The criteria for the list that this summit relocation applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub category entitled the 200m Sub-Twmpau consisting of all Welsh hills at or above 200m and below 300m in height that have 20m or more and below 30m of drop.  With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Top and this was derived from the Tithe map, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads, with also the B4389 and B4390 roads to its east, and has the village of Adfa towards the south.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the accompanying 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-assessed and it was listed with 26m of drop, based on the 269m 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 which is now presented on the mapping on the Magic Maps website and which is positioned at SJ 06183 01659, and the 243m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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.

LIDAR analysis shows the ground at the base of a raised field boundary to be the highest on the hill, however as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill in the listings I author.  LIDAR analysis also shows the position of the natural summit of this hill and this has now been surveyed with the Trimble GeoXH 6000 and it is this result that is being prioritised for this hill.

LIDAR summit image of Cae Top

The summit height and position produced by the Trimble GeoXH 6000 survey is 268.8m at SJ 06132 01671, and this position in relation to the raised field boundary shown by LIDAR analysis comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the hill’s high point is in a different field, or where a number of potential summit positions are within close proximity and the highest point is not where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour, or when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

The Trimble GeoXH 6000 gathering data at the summit of Cae Top

Therefore, the new listed summit height for this hill is 268.8m and is positioned at SJ 06132 01671, this position is given a spot height on the Magic Maps website and is approximately 50 metres from where LIDAR gives the high point of the raised field boundary.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Carnedd Wen

Name:  Cae Top

OS 1:50,000 map:  136

Summit Height:  268.8m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference (new position):  SJ 06132 01671 (Trimble GeoXH 6000)

Bwlch Height:  243.0m (LIDAR)

Bwlch Grid Reference:  SJ 06613 01642 (LIDAR)

Drop:  25.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (November 2020)