Wednesday, 7 October 2026

Mapping Mountains – Trimble Surveys – Mynydd Epynt

 

07.06.26  Ysgwydd Hwch (SO 052 379), Lan (SO 052 391) and Yr Allt (SO 059 390)

Yr Allt (SO 059 390)

This year’s Relative Hills Society (RHSoc) dinner was held in The Wellington Hotel in Brecon.  It was the first time I had attended since my guest speaker slot at Shifnal a few years ago.  The evening was very enjoyable and especially so as our Y Pedwarau table won the quiz.  Afterward I sauntered back to my car to find a quiet spot to overnight.  This was next to a waste disposal site, which doesn’t sound very pleasant, but the area was quiet and out of the way with only one car passing the junction at the end of the road as I prepared my bed for the night with stars appearing in a clearing sky.  The following morning after boiled eggs and samosas for breakfast I drove to Talgarth to the New Gurkha Inn to meet Mark Trengove, who had over-nighted there.  After his breakfast and packing his car we headed off to the hills. 

A nice quiet spot to spend the night

Our plan for the day were three forested Pedwar hills to the north of Talgarth, and as the days forecast gave strong blustery wind the confines of the forest would at least give us shelter.  Our first attempt at finding our parking place ended in failure with me leading the way and trying to navigate with an OS map.  We ended up back on a main road having driven about six miles on narrow country lanes.  Our second attempt was led by Mark using his SatNav, this thankfully proved successful and soon my car was parked at the start/end of a forest track to the north-east of the small community of Llaneglwys.  Mark then drove to the start of our walk which had a convenient small parking area and picnic tables.

Close to where Mark parked his car was the forest track leading to our first hill of the day.  We set off walking at 10.40am, with the wind blowing and if the forecast was correct, dry overhead conditions until late in the afternoon when more rain was predicted to head in from the west.

A clearing on our left gave views looking south toward the high Beacons, except for Pen y Fan all just clear of the grey murking cloud.  It made a tranquil scene with greened fields as foreground, and all the more so as we didn’t expect many opportunities for extensive views during the entirety of the walk due to the confines of the conifer plantation we were now walking up in to. 

Looking out toward the high Beacons

As we approached the first summit and our high point of the day; Ysgwydd Hwch, we encountered a section of felled forestry, this gave a semblance of view.  But as usual such places are scattered with tree debris that is both an unruly mess to look at and also a hell to walk through.  Thankfully the continuation of the access track we were now on which led toward a tall mast and small compound made our upward progress relatively easy. 

Mark heading on the access track toward the summit of Ysgwydd Hwch

Approaching the summit of Ysgwydd Hwch

The area of the high point was not difficult to find and aided by the ten figure grid reference attained from LIDAR analysis we were soon standing on the summit.  Shortly afterward I had the Trimble assembled and gathering data.  However, as I stood below the equipment I considered this position to consist of accumulated debris and therefore man-made, because of this I took a second data set a few metres away at the base of a tree stump. 

Gathering data at the first of two set-up positions at the summit of Ysgwydd Hwch

Once data were gathered and stored I closed the equipment down and as I was just getting ready to take a few photographs I saw a figure standing beside the edge of the small compound enclosing the mast, he was smiling and waving my way; it was Alex Cameron who had also been at the dinner last night and who was on one of his mammoth overnight walks with these same three hills his destination.  I hadn’t seen Alex on the hill in quite some time and although Mark and I had wondered if any other fellow hill bagger may be on these hills today, it was still a surprise to see him.  Hugs were had and we continued the rest of the walk as a threesome. 

The second of two set-up positions at the summit of Ysgwydd Hwch with Alex the unexpected visitor in the background

Our onward route was now following forest tracks north-eastward before swinging west where our track bisected another coming in from the south which was an alternate option to get us from the summit of Ysgwydd Hwch to this point.  On the way the view opened toward our next two hills.  From this direction they looked deeply forested, but thankfully the trees on each were mature and proved easy to walk through and therefore reach the summit of each hill.  All around was greenery with succulent ferns and moss encrusted old branches backed by the strong wisps of wind that cascaded over the hills. 

On the forest track between Ysgwydd Hwch and the small pool

Summer greenery

Lan (SO 052 391)

As we lost height part of the forest had been felled with the diggers in situ awaiting the next working day and the logs neatly stacked awaiting removal.  Close to was a small pool that Mark had spotted, we stood beside it for a few minutes enjoying the tranquil scene. 

The forest track leading down toward the small pool

Mark beside the small pool

The next part of the walk was back on to the continuation of the forest track as it headed uphill.  For me I was now in head down and plodding mode.  Gone are the days when I could tackle such ascents relatively easy and quickly, a sad indictment of getting older when the body and its capabilities change.  Soon we turned right on to a green track which in time led to a narrow path on our right leading in to the main conifer plantation.  The narrow path was part of a series of mountain bike trails through these woods, with others evident in a few places.  All were welcome and this one was a delight to walk on as it took us forever higher through the wood.  The path eventually swung around and ended up within a few metres of the high point of this our second hill of the day. 

Entering the wood on our way to the summit of Lan

This hill was originally listed by the name of Llaneglwys Wood.  A name I invented when the Welsh 400m hills were first compiled.  Its listed name was changed to Lan in 2016 when Aled consulted the Tithe map and this is how it has appeared in the Y Pedwarau – The 400m Hills of Wales list ever since. 

The Trimble GeoXH 6000 positioned at the summit of Lan

Having reached the top it was time to have a rest.  Alex sat and took his boots off to give his feet time to heal from those many hours of overnight walking, whilst Mark and I pottered about checking grid references and judging any potential high point for their claim to be the summit position of the hill.  Having chosen our preferred candidate I positioned the Trimble on top for the customary photograph.  I had no intention of trying to gather data from this summit due to the overhead canopy of trees and therefore soon joined the others for a restful few minutes having lunch. 

Time to rest

As the remains of my treats consisting of a Polish sausage and oat biscuits were packed away, it was time to set off and Alex led the way on the continuation of the narrow mountain bike trail as it quickly lost height heading in the direction of the green track that had given us access to the upper part of the hill.  The path was more indistinct on this side of the hill, but nonetheless still easy to follow. 

Heading down from the summit back on to the green track

Having regained the green track, it soon veered left and then immediately right and now continued with an open field on our right.  This part of the walk I found particularly beautiful as the long grass in the field swayed to the rhythm of the wind.  We stopped to take photos of the conifered upper part of our last hill of the day; Yr Allt which is another name derived from the Tithe, with the farm to the south giving the name of the hill away; Danyrallt, under the allt. 

Yr Allt from the connecting green track between it and Lan

By now I was progressively getting slower compared to Alex and Mark.  Alex is a strong walker and even with a large heavy rucksack was much quicker than me during the whole walk, whilst Mark is a good steady walker and who kindly waited for me to come in to view at any major turn to make sure that I did not overshoot as I brought up the rear. 

On the green track leading to the narrow path on our right in to the wood

We now headed in to the wood on what looked like a form of path; however we soon left this and headed up through the trees with Mark guiding the way toward the summit with the aid of his hand-held GPS.  Thankfully the summits of Lan and Yr Allt are both within mature forest, making walking between the trees easy.  I found this delightful and such a change from what can become an unruly obstacle course when further progress up or many times even down, seems next to impossible due to the confines of conifer trees. 

Extraordinary mosses on our way through the wood to the summit of Lan

Having reached the summit we did the customary things, stopped, chatted, took a few photos and then debated the best way to get off the hill and back to my awaiting car.  We had a couple of options and eventually decided to backtrack to the inward green track, this continued down the hill but was seemingly barred from further progress due to one of the rare felled trees across the path that we encountered during the day.  Mark considered backtracking and taking a detour, but thankfully Alex went ahead to investigate and once on the other side called us on. 

The summit of Lan

The green track swung southward around the eastern face of Yr Allt and then doubled back on itself now heading north-eastward and all the time loosing height.  This again was a delightful part of the walk, easy underfoot with occasional brambles and nettles to bi-pass, all of which were easy to avoid and all the time the greenery of summer was on display with succulent growth appearing all around.

We were nearing the end of the walk; all that remained was finding a way down on our right either over a barb wired fence giving access through a long grassed field down to the minor road close to where my car was parked, or another route down which Alex and Mark were now investigating.  This consisted of yet another delightful narrow path on the edge of the wood and beside the boundary fence with the field beyond. 

Mark on the narrow path leading back to the forest track and the car

We stopped for a few minutes as the view opened toward the masted summit of Ysgwydd Hwch.  From this direction the whole upper hill seemed to consist of a mass of confined forestry, as indeed all three hills seemed to be so from a distance.  Thankfully for the enjoyment of today’s walk each proved otherwise. 

Ysgwydd Hwch (SO 052 379)

We were soon at my car, and a few minutes later at Mark’s car at the small picnic area.  All that remained was the drive back to Welshpool and three welcome mugs of tea before Mark took Alex to Flint railway station for his train home.  It had been another good day on the hill in the company of two good friends with another three Pedwar hills visited. 

 

Survey Result:

 

Ysgwydd Hwch

Summit Height:  455.7m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SO 05233 37909 (Trimble GeoXH 6000) 

Bwlch Height:  386.6m (LIDAR)

Bwlch Grid Reference:  SO 03872 38847 (LIDAR)

Drop:  69.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  15.15% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

Lan (significant name change)

Summit Height:  413.9m (LIDAR) (significant height revisions) 

Summit Grid Reference:  SO 05239 39141 (LIDAR) 

Bwlch Height:  377.2m (LIDAR)

Bwlch Grid Reference:  SO 04853 39386 (LIDAR)

Drop:  36.7m (LIDAR) (400m Sub-Pedwar reclassified to Pedwar)

Dominance:  8.87% (LIDAR)

 

 

Yr Allt (significant name change)

Summit Height:  407.0m (LIDAR) 

Summit Grid Reference:  SO 05914 39093 (LIDAR) 

Bwlch Height:  364.7m (LIDAR)

Bwlch Grid Reference:  SO 05578 39234 (LIDAR)

Drop:  42.3m (LIDAR)

Dominance:  10.39% (LIDAR)

 


My thanks to Alan Dawson with help processing these data


For further details please consult the Trimble Survey Spreadsheet

Sunday, 4 October 2026

Mapping Mountains – Significant Height Revisions – The Welsh P15s

 

Braich Bryn Engan (SH 723 569) 

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

LIDAR image of Braich Bryn Engan (SH 723 569)

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 10th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Braich Bryn Engan, and it is adjoined to the Moel Siabod group of hills, which are situated in the north-western part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the A4086 road to its north-west and the A5 road to its north-east, and has the village of Capel Curig towards the north.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included in either the main list or the accompanying sub list, with subsequent interpolation giving the hill an estimated c 336m summit height and an estimated c 323m bwlch height, with both heights based on interpolation of 10m contouring. 

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 Braich Bryn Engan (SH 723 569)

The summit height produced by LIDAR analysis is 338.1m and when compared to the previously listed summit height, this comes within the parameters of the Significant Height Revisions used within this page heading, and these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive 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 with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 338.1m and this was derived from LIDAR analysis.  This is 2.1m higher than the previous listed summit height of c 336m, which was based on interpolation of the uppermost 330m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Moel Siabod 

Name:  Braich Bryn Engam 

OS 1:50,000 map:  115

Summit Height (New Height):  338.1m (LIDAR)                                                           

Summit Grid Reference:  SH 72354 56932 (LIDAR)                                                  

Bwlch Height:  319.8m (LIDAR) 

Bwlch Grid Reference:  SH 72162 56912 (LIDAR) 

Drop:  18.4m (LIDAR) 

                                                           

Myrddyn Phillips (October 2026)

Thursday, 1 October 2026

Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales


Boncyn Nadroedd (SJ 027 540) – 390m Double Sub-Pedwar reinstatement

There has been a reinstatement of a hill to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Boncyn Nadroedd (SJ 027 540)

The criteria for the list that this reinstatement applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being reinstated to the 390m Double Sub-Pedwar category.  The criteria for this sub category being all Welsh hills at or above 390m and below 400m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Boncyn Nadroedd and it is adjoined to the Mynydd Hiraethog group of hills which are situated in the north-eastern part of North Wales (Region C1, Sub-Region C1A), and it is positioned with minor roads to its north, west and east, and has the town of Rhuthun (Ruthin) towards the east north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category.

When 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 23m of drop, based on an estimated c 390m summit height and an estimated c 367m bwlch height, with each based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, and these were the details that it appeared under after the 390m sub categories were added to this list. 

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

The details for this hill were re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This re-assessment resulted in the estimated bwlch height for this hill being amended to c 368m, with this based on interpolation of 5m contouring between 365m – 370m. 

Extract from the Magic Maps website

The details for this hill were also re-assessed against Ordnance Survey data hosted on the Magic Maps website as well as the WalkLakes website, and what was thought to be a tiny uppermost 390m summit ring contour is given a 389m spot height on these two interactive maps, implying that what was taken as a small ring contour on the Ordnance Survey 1:25,000 Explorer map, is in fact a spot height missing its 389m height, resulting in the deletion of this hill from 390m Double Sub-Pedwar status. 

Extract from the WalkLakes 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.

Therefore, the reinstatement of this hill to 390m Double Sub-Pedwar status is due to LIDAR analysis, resulting in a 390.0m summit height and a 368.4m bwlch height, with these values giving this hill 21.6m of drop, which is sufficient for it to be classified as a 390m Double Sub-Pedwar. 

 

The full details for the hill are:

Group:  Mynydd Hiraethog 

Name:  Boncyn Nadroedd 

OS 1:50,000 map:  116

Summit Height:  390.0m (LIDAR) 

Summit Grid Reference:  SJ 02735 54033 (LIDAR) 

Bwlch Height:  368.4m (LIDAR) 

Bwlch Grid Reference:  SJ 02555 54073 (LIDAR) 

Drop:  21.6m (LIDAR)

 

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

 

Y Pedwarau

 

Y Pedwarau – 400m Sub-Pedwarau

 

Y Pedwarau – 390m Sub-Pedwarau

 

Y Pedwarau – 390m Double Sub-Pedwarau

 

Myrddyn Phillips and Aled Williams (October 2026)