Why do summits get deleted?
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Because they no longer qualify. Typically another summit is found to be more prominent or re-measurement shows the summit to be less prominent.
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Aha!
Although some SOTA summits in GM no longer have the 150m prominence to qualify as SOTA summits, I am aware also that some new hills in GM have been found to now have 150m prominence so I expect that these will become SOTA summits.
Jimmy M0HGY
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Thats cool, but surprises me, as I thought that everything would have been surveyed with accurate gps by now, although as I type this I do recall some chaps trying to get an extra Munro or Top out of Ben Avon a couple of years ago. They didn’t succeed.
No. The vast majority was surveyed with levels and theodolites by the 60s. The OS gave up using all trig points many years back and now just use a small subset of them along with many other GPS benchmarks. So yes they have an updated model and are always checking and improving accuracy. They don’t have a good business reason to remeasure Munros etc. to ensure they are accurate to 1cm.
Most of the changes in the UK are the result of a bunch of guys in the RHB (Relative Hills of Britain) group known as The Tamperers. The have survey grade GPS gear and produce results of such accuracy that the OS will update map data from their submissions. For them, prominence is important and they have been measuring summits where the P value is 140-160m as these are most likely when resurveyed to result in additions/deletions from the lists. Likewise checking with double summits which is the higher etc.
Some of the changes coming up in GM are the result of accurate surveying and finding one summit is actually 20cms lower than believed resulting the true summit moving about 500m to the other summit. For some the P value has been measured as only being 149.4m i.e. 60cm too small and so the summit is deleted.
The errors are small, most under 50cms, that the urgency to update the association is not justified especially as I do other SOTA jobs. But they’ve been festering for a while now so it’s time to get them done.
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That’s the guys i was thinking of.
Thanks for the detailed explanation.
|nteresting. `My wife thinks SOTA is a bit nerdy. Wait till I tell her about the RHB group.
But on a practical level I notice they are capable of measuring with such accuracy (you mention 60cm for example), I wonder how, they deal with cairns, rocks or archeological tumuli given that they can significantly alter whether a particular prominence is either included or excluded?
David
To a few cms in fact. It’s worth checking out their Groups.io pages and see how the do things. I thought I was a pedant as are many on here but some of the RHB take pedantry to new heights (no pun intended) and you have to admire that 
They have just remeasured The Coyles Of Muick GM/ES-050 to be 599.2m from the OS stated height of 601m (OS 1:50k) or 596m (OS 1:25k). I think that that height is accurate to 10cms.
I can recommend Coyles Of Muick as a cracking little summit.
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You can also wave at Chas & Camilla on the way up there 
Ah yes, Fred & Gladys. But you wont catch a glimpse of Haz & Megs any more.
I did GM/ES-050 the year before last. Lovely summit and excellent view. Even the walk up was interesting.
Not if you’re going to delete it! 
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As far as I am aware, this list below are the changes that I am aware of in GM and this mentioned summit isn’t going to be one of the ones to be deleted.
Carn Liath GM/ES-020 is replaced by Creag an Dail Bheag (new GM/ES Marilyn).
Beinn Dearg GM/SS-067 is replaced by Creag na h-Eararuidh (new GM/SS Marilyn).
GM/WS-053 - summit relocation from Maoile Lunndaidh to Creag Toll a’Choin. No deletion or addition required as col between both these summits are within activation zone. I think there similar SOTA summits in GM where the summit location has changed, but SOTA reference number can stay the same due to old and new summit locations being within activation zone of each other.
Creag an Amalaidh - new Marilyn in GM/NS.
Cruim Leacainn GM/WS-344 - no longer a Marilyn.
Troweir Hill GM/SS-257
Sithean Mor - New Marilyn in GM/WS,
Kirriereoch Hill - New Marilyn in GM/SS.
Stob na Boine Druim-fhinn G/SS-089
Beinn Dearg - new Marilyn in GM/NS
White Hill is now twinned with Hightown Hill GM/SS-273 and according to Hill-Bagging White Hill is now the Marilyn and Hightown Hill GM/SS-273 is the twin Hightown Hill (hill-bagging.co.uk) White Hill (hill-bagging.co.uk). I think from this Hightown Hill GM/SS-273 would need to be deleted and White Hill becomes a new SOTA summit in GM/SS.
I also know that although this isn’t affected as such in terms of a SOTA point of view, but Cnoc Coinnich GM/SS-046 has increased in height and become a Corbett, see GM Marilyn is now a Corbett - Summit Info - SOTA Reflector. I am sure that heights have changed for plenty of other GM SOTA summits also due to more accurate surveying in recent years.
I am sure that the GM - Association Manager Andy MM0FMF will point out any changes that I’m not aware of when he announces the changes officially.
Jimmy M0HGY
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Sadly all that effort in 2016 to survey Cnoc Coinnich hasn’t changed much. The online OS mapping app I have is still showing the old height of 761m. 
Edit: Just noticed the 764m height is shown correctly on the 1:25K map but 761m is still shown on the 1:50K map.
Thanks for the update. I did expect the above one. That’ll add another 2km onto what is already a long hike for someone doing it along with Culardoch GM/ES-015
Do them separately then. Just because there are 2 summits reasonably close doesn’t mean they have to be done in the same session. That pair are an obvious candidate for bike access especially as I have done the walk in 2 and half times.
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It has just been announced that Giur-bheinn GM/SI-142 is not longer Marilyn so therefore will be another GM SOTA summit that will need to be deleted.
"Alan Dawson ad.staclee@gmail.com
Tue 25/05/2021 21:06
To:
News from Islay:
Giur-bheinn is no longer a Marilyn. It is not in the RHB book but was added to the list in 1995 after an OS map increased its height from 316m to 318m, tilting the probability in its favour. I was finally able to survey it recently.
Summit 317.4m at NR 3798 7286
Col 168.5m at NR 4008 7581
Drop 148.9m
The result is no surprise as its status was always marginal. This may or may not be the last Marilyn demotion. Cliffe Hill in Sussex is highly marginal but retains its status at present.
Alan"
You will see that it mentioned that Cliffe Hill G/SE-014 is highly marginal but remains a Marilyn for the time being, if this hill looses its Marilyn status, this will also need to be deleted from the SOTA programme. Cheriton Hill G/SE-015 is confirmed to be no longer a Marilyn and will be removed from the SOTA programme after the 31st August.
Jimmy M0HGY
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