Mapping Mountains – Significant Height Revisions – Y Pedwarau

Pawl Hir (SO 101 595)

There has been a Significant Height Revision to a hill that was surveyed for 400m Sub-Pedwar status with the Trimble GeoXH 6000, with the survey that resulted in this significant height revision taking place on the 3^rd October 2017 in good, clear conditions.

The criteria for the list this hill was surveyed for are:

Y Pedwarau – All Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.  Whilst the criteria for 400m Sub-Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Pawl Hir and it is situated in the Fforest Glud range of hills which are in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and the hill is positioned between the town of Llandrindod (Llandrindod Wells) to its west north-west and the small community of Hundred House to its south.

Pawl Hir (SO 101 595)

As the summit of the hill is not on designated open access land permission to visit should be sought, for those wishing to do so the nearest public footpath crosses the hill from a west – east direction and just bi-passes the two high points of the hill, one of which is situated on the northern part of the summit area and the other on the southern part, with the easiest and most convenient ascent being from the east following the footpath up the hill from the convenience of a sharp corner on a minor lane, where there is adequate parking for a car.

Prior to the survey with the Trimble GeoXH 6000 the hill was noted with 19m of drop based on the 408m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and the 389m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website, this latter map also gives a 407m spot height to the south south-west of the 408m summit spot height.  Therefore, the purpose of the survey was to ascertain the high point of the hill and determine if it had the minimum of 20m of drop required to be classified as a 400m Sub-Pedwar.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

In all four points were surveyed for the high point of this hill; one on the northerly land where the 408m spot height appears and three on the southerly land where the 407m spot height appears, these results are given below:

1^st survey, 408m spot height – 404.903m (converted to OSGM15) at SO 10225 59703

2^nd survey, 407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

3^rd survey, 407m spot height – 405.359m (converted to OSGM15) at SO 10036 59429

4^th survey, 407m spot height – 405.641m (converted to OSGM15) at SO 10027 59400

Although the three survey results obtained on the southerly high point of this hill do not come within the parameters of the Significant Height Revisions used within this page heading, the survey result obtained on the northerly high point does, and therefore this is worth recording, these parameters are:

The term Significant Height Revisions applies to any listed hill whose 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, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

The highest height obtained with the Trimble GeoXH 6000 compared to where each spot height appears on the ground is given below:

408m spot height - 404.903m (converted to OSGM15) at SO 10225 59703

407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

Although the position where the 408m spot height appears on the ground is not the high point of the hill, the result produced by the Trimble GeoXH 6000 for this position does come within the above parameters.  

Therefore, this hill’s new summit height is 405.8m (converted to OSGM15) which is positioned on the southerly land of this hill’s summit area, whilst the 404.9m (converted to OSGM15) surveyed height which is positioned on the northerly land of this hill’s summit area is 3.1m lower than the Ordnance Survey 408m spot height that appears on the 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill:  Gilwern Hill

Summit Height (New Height):  405.8m (converted to OSGM15)

Name:  Pawl Hir

OS 1:50,000 map:  148

Summit Grid Reference:  SO 10108 59510

Drop:  16.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the northerly high point of this hill which resulted in this point's significant height revision

For details on the survey that ascertained an accurate summit height for this hill

Myrddyn Phillips and Aled Williams (December 2017)