Mapping Mountains – Significant Height Revisions – 200m Twmpau

Chwarel Penrhyn (SH 621 658) 

There has been a Significant Height Revision 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 derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Chwarel Penrhyn (SH 621 658)

The criteria for the list that this height revision 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 list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Chwarel Penrhyn, and it is adjoined to the Glyder Fawr 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 B4409 road to its north, a minor road to its west and the A5 road to its east, and has the town of Bethesda towards the north-east.

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 with no significant contours of note on the contemporary Ordnance Survey 1:25,000 map, it was hard to know whether any hill with qualifying prominence existed and therefore it was considered not to meet the criteria then used for this sub category. 

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 Chwarel Penrhyn (SH 621 658)

LIDAR analysis gives the summit of this hill as 220.6m positioned at SH 62149 65875, 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, 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 220.6m and this was derived from LIDAR analysis, this is 70.6m higher than the highest contour in the vicinity of this hill that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyder Fawr 

Name:  Chwarel Penrhyn 

OS 1:50,000 map:  115

Summit Height (New Height):  220.6m (LIDAR) 

Summit Grid Reference:  SH 62149 65875 (LIDAR) 

Bwlch Height:  197.0m (LIDAR) 

Bwlch Grid Reference:  SH 61793 65966 (LIDAR) 

Drop:  23.6m (LIDAR)

Myrddyn Phillips (January 2026) 

Mapping Mountains – Trimble Surveys – Arenig Fawr

13.12.25  Ffridd Trawsgoed (SH 837 328) and Moel Hafod yr Ŵyn (SH 841 322) 

Moel Hafod yr Ŵyn (SH 841 322)

There is bleak beauty in venturing on to rough, unremitting ground and especially so during the onset of winter where grey skies predominate and a brisk wind echoes across the land.

Today we visited two hills positioned just west of the southern most part of Llyn Tegid.  Both are relatively easy to access from the narrow road that winds its way across these hills toward Bronaber.  I hadn’t been on this road in many years and had not until today visited these two hills.

I met Mark and Aled in Y Bala, where we left two cars and then continued on the A494 road heading south-west beside the lake toward the minor road that in time would take us to our designated parking spot on a grass verge beside an old metal gate. 

Heading toward the forest track

The forecast gave south-westerly winds, so not chilled and relatively mild for the time of year.  I set off before Mark and Aled, but soon stopped and waited as the continuation of the way up the hill was indistinct with slender long grasses amongst bracken and stunted trees giving little indication of a path.  However, one did exist and once on it I followed my companions up to a forest track that shortly afterward bisected another track where a person was standing beside a gate.  As we approached we said hello; Andrew Graham was the landowner, his sister was standing a short distance further down the track.  We chatted for five minutes or so, he was concerned as the gate had been left open and wondered who had done it.  He’d come to the area in the 1960s having bought the land to turn it over to the conifer plantation that now surrounded us. 

Andrew Graham

As Andrew walked down the track to join his sister, we headed in the opposite direction looking for a convenient access point on to the upper hill, which now rose in front of us a mass of heather and roughness.  The going uphill from this point was steep and ponderous with no semblance of path.  It was hard work, but also a marvelous place to find oneself on a Saturday afternoon in December. 

The steep heathery slopes leading to the summit of Ffridd Trawsgoed

I arrived on top last out of the three and was immediately buffeted by the brisk wind.  Although I’d brought the Trimble I had little intention of using it unless the tops were covered in clag and then only as a hand-held GPS device.  However, I still placed it on the high point for the customary photograph. 

The summit of Ffridd Trawsgoed

To our south Moel Hafod yr Ŵyn looked a wild inviting hill, with a rather unpleasant bog between us and it.  Leaving the summit we stumbled our way down the steep pathless slope and back on to the relative comfort of the forest track.  However, the comfort didn’t last long as soon the bog would have to be tackled. 

Moel Hafod yr Ŵyn and its unsavoury looking bog

There’s a pleasing aspect to bogs.  Many are lush with copious amounts of undergrowth and this one was definitely one to savour.  Progress through it was never difficult and wearing vibram soled wellies certainly helped.  I followed Aled as he furrowed his way through, only stopping occasionally to regather my breath during which I looked at the slender threads of long grasses as they gently danced in the wind.  As I said; there is beauty in a bog. 

Mark tackling the bog

Mark soon joined us on the other side of the bog and as Aled headed up to gain height, Mark continued flanking the upper hill on the periphery of the bog before then heading up toward the summit cone.  Oh decisions decisions, what one to follow?  I opted for Aled and was soon being left behind as I made slow progress through the undergrowth.  By the time I spotted Mark he had gained height and was approaching the upper part of the hill, Aled was already nearing the summit.  I continued my slow plod up in to the realms of wind and views.

Aled heading toward the summit of Moel Hafod yr Ŵyn

The upper cone of Moel Hafod yr Ŵyn

The upper hill proved a delight with a small rock band to veer past.  Having reached the summit I did as I had done on top of Ffridd Trawsgoed and placed the Trimble on the high point for its customary photograph.  The view compensated for my tiredness, with the land to the west a wild and remote place of more tussocks, bog and rising hills, whilst to our south-east the descending slopes headed down to the gentler climes of the valley below. 

The summit of Moel Hafod yr Ŵyn

Leaving the high point I followed Aled down through mixed ground of heather and intermittent hidden rock.  Our route down led to a wall which had a barb wired fence perched menacingly on top of it.  This was not good news for the two elderly gentlemen in our walking party.  However, with the help of our younger colleague there was no mishap and soon we were standing on relatively safe ground on the other side. 

The last steep slope leading back on to the narrow road and the car parked beyond

From here it was only a short walk back to the car; with an initial steep slope leading on to the narrow road where we veered right and followed the thin width of tarmac a few hundred metres back to where we had started our walk from.

We were back in Y Bala at around 4.40pm and soon happily seated in the Plan yn Dre for an early evening festive meal, which proved an excellent way to end another good day on the hill. 

 

Survey Result: 

 

Ffridd Trawsgoed 

Summit Height:  423.9m (LIDAR)  

Summit Grid Reference:  SH 83755 32841 (LIDAR)

Bwlch Height:  384.2m (LIDAR)

Bwlch Grid Reference:  SH 83731 33086 (LIDAR) 

Drop:  39.7m (LIDAR)

Dominance:  9.36% (LIDAR)

 

 

Moel Hafod yr Ŵyn 

Summit Height:  398.2m (LIDAR) (significant height revision)  

Summit Grid Reference:  SH 84199 32238 (LIDAR)

Bwlch Height:  358.4m (LIDAR)

Bwlch Grid Reference:  SH 84033 32465 (LIDAR) 

Drop:  39.8m (LIDAR)

Dominance:  9.99% (LIDAR)

 

 

For further details please consult the Trimble Survey Spreadsheet 

Mapping Mountains – Summit Relocations – The Fours – The 400m Hills of England

Burton Howe (NZ 607 032) 

There has been a Summit Relocation to a hill that is listed in the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Burton Howe (NZ 607 032)

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

The Fours – The 400m Hills of England - English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is now listed by is Burton Howe, and it is adjoined to the Urra Moor group of hills, which are situated in the North York Moors of north-eastern England, and it is positioned with minor roads to its north and east, and the B1257 road to its west, and has the town of Stokesley towards the north-west.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10^th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop.

Prior to this revision this hill was listed under the name of Greenhow Moor with 17m of drop, based on the 432m summit spot height positioned at NZ 61114 02607 and the 415m col spot height that appear on the Ordnance Survey 1:25,000 Explorer map. 

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 Burton Howe (NZ 607 032)

LIDAR analysis gives the highest ground on this hill as 432.3m positioned at NZ 60792 03254, and when compared to its originally listed summit position which LIDAR gives as 432.2m positioned at NZ 61049 02611 and NZ 61062 02608 and NZ 61063 02601 and NZ 61063 02599 and NZ 61080 02598 this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, 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 or covered reservoir that is considered a relatively recent man-made construct, or the listing of a new twin summit or de-twinning of a summit, 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.

Therefore, the summit height produced by LIDAR analysis is 432.3m and this is positioned at NZ 60792 03254.  This position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 650 metres north north-westward from where the originally listed summit is positioned.

 

The full details for the hill are:

Group:  Urra Moor

Name:  Burton Howe

OS 1:50,000 map:  94

Summit Height:  432.3m (LIDAR)

Summit Grid Reference (New Position):  NZ 60792 03254 (LIDAR)

Col Height:  415.4m (LIDAR)

Col Grid Reference:  NZ 62245 02507 (LIDAR)

Drop:  16.9m (LIDAR)

 

Myrddyn Phillips and Aled Williams (January 2026) 

Mapping Mountains – Significant Name Changes – 100m Twmpau

Ffridd Defaid (SN 663 983) 

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau, 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 Ffridd Defaid (SN 663 983)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The hill is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road and the A493 road to its south, and has the small community of Cwrt towards the north-east.

When the original 100m 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, as it was considered not to meet the criteria then used for this sub category.

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 under the point (Pt. 196m) notation with an estimated c 22m of drop, based on the 196m 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 174m bwlch height, based on interpolation of 10m contouring between 170m – 180m. 

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 470 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 Ffridd Defaid the apportionments, with the details on the Tithe map appearing in the parish named as Tywyn and in the county named as Merioneth. 

Extract from the apportionments

Therefore, the name this hill is now listed by in the 100m Twmpau is Ffridd Defaid, and this was derived from the Tithe map. 

 

The full details for the hill are:

Group:  Tarren y Gesail

Name:  Ffridd Defaid

Previously Listed Name:  Pt. 196m   

OS 1:50,000 map:  135

Summit Height:  196.6m (LIDAR) 

Summit Grid Reference:  SN 66387 98356 (LIDAR) 

Bwlch Height:  174.9m (LIDAR) 

Bwlch Grid Reference:  SN 66339 98328 (LIDAR) 

Drop:  21.7m (LIDAR) 

 

Myrddyn Phillips (January 2026) 

Mapping Mountains – Trimble Surveys – Carnedd Wen

 

20.11.25  Gaer Fawr (SJ 223 129, previously Trimbled)

Gaer Fawr (SN 223 129)

Gaer Fawr stands as a large mound of a wooded hill on the periphery of Guilsfield.  The trees hide its true significance as one of Wales’ great ancient hill forts.  When occupied it had up to five lines of ramparts, with some 8m in height.

The wood surrounding the hill is now managed by the Woodland Trust and today’s visit was with my cousin Lynn.  Since our last visit in May 2021, Lynn had donated a large sum to the Woodland Trust from a trust fund set up in memory of her late husband; Dave.  Part of the donation went toward installing a bench overlooking the eastern aspect of the hill toward Cefn Digoll off in the distance.  Therefore, as well as enjoying Lynn’s company whilst taking in a small walk, she wanted to show me the bench set up in Dave’s memory.

Having left my car in the parking area beside a small quarry we headed back down the narrow lane that leads toward the south-westerly lower part of the hill.  The weather was set fine, albeit with a chilled easterly breeze.  However, during our walk we were sheltered from this in the wood.

There are a number of paths through the wood, all seem to connect with ones leading to the summit which I’d previously Trimbled.  Our route for the day led back down the narrow road to a gate giving access to the lower eastern part of the wood. 

Lynn on the path heading through the wood

It was good to be out with Lynn again, a person whose company I’ve enjoyed on small walks over recent years.  The path circled the easterly part of the wood, gaining height as it did so, before swinging up in to the canopy of trees that shone dappled light whenever the sun broke through intermittent cloud. 

The bench set up with one of Lynn's donations to the Woodland Trust

Our route led us straight to the bench.  It was an ideal place to stop and rest.  From this position a gap in the trees looked out toward the east.  Just behind us another path led up to connect with one of the main routes to the summit.  The bench had been placed in a quiet spot, one for rest and contemplation.  A small plaque on it had an inscription from one of Lynn’s favourite poems which she read for me; Fern Hill by Dylan Thomas, ‘and once below a time I lordly had the trees and leaves’.  I took a few photos before we left to head up the path toward the summit. 

The plaque in memory of Lynn's late husband

Although the summit area is open there is no extensive view due to surrounding trees.  However, it is a beautiful place to visit and especially so in May when blue bells adorn the ground. 

The summit of Gaer Fawr (SJ 223 129)

We both wandered, me enjoying the dappled low light casting deep shadow and emerald colour through the trees and Lynn looking out through the trees to the lands beyond.  We left heading down to visit the large terracotta wild boar that commemorates the bronze boar helmet found at this site that is positioned near the top of the ancient north-east entrance. 

The terracotta boar

Leaving the wild boar we took the path down, opting for the longer route that contours the lower part of the wood leading back to the small quarry and the awaiting car.  By the time we arrived the temperature had chilled with late afternoon heralding another cold frost encrusted night. 

    

Survey Result: 

 

Gaer Fawr (significant name change)

Summit Height:  217.6m (converted to OSGM15, from previous Trimble GeoXH 6000 survey) 

Summit Grid Reference:  SJ 22394 12995 (from previous Trimble GeoXH 6000 survey) 

Bwlch Height:  138.7m (LIDAR)

Bwlch Grid Reference:  SJ 21991 13145 (LIDAR)

Drop:  78.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  36.26% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For details on the 1^st survey of Gaer Fawr

For details on the 2^nd survey of Gaer Fawr

For details on the 3^rd visit to Gaer Fawr

 

 

For further details please consult the Trimble Survey Spreadsheet