Last year I did an extract of summits from sotlas and downloaded them as a GPX file to my GPS. I have only owned a GPS for around a year and still only use it to confirm summit locations on ambiguous summits.
I recall during my activation of GM/WS-011 the gpx location was debatable as to whether it was even within the AZ.
Fast forward to last week and I experienced a larger error on GM/SI-014.
I have done some digging and my gpx file extracted from sotlas (from last year dated 2021-06-18T13:23:20.026Z) has the following for GM/SI-014.
The current lat/lon values are provided from the Relative Hills of Britain download. Previous values would have been sourced from a coordinate conversion of the 6-figure grid reference. The conversion itself was possibly not so precise and anyway the gridref (from RHoB) was updated. So yes, it’s good to watch out for our (monthly) announcements and take special note when we say there were position tweaks to your association:
I don’t have easy access to the data to quantify how many of these were outside of the activation zone.
I filtered any change > 150 m:
GM/CS-043 - Geal-charn, 162.3 m GM/CS-069 - An Dun, 369.5m GM/CS-083 - Meall na Leitreach, 156.0 m GM/NS-142 - Cnoc an Daimh Mor, 197.1 m GM/NS-144 - Creag a’Ghobhair, 498.2 m GM/SI-068 - Sgurr na Stri, 181.0 m GM/SI-090 - Beinn Bhreac, 367.0 m GM/SI-108 - Guainemol, 187.7 m GM/SI-123 - Beinn Chreagach, 301.7 m GM/SI-205 - Sotan, 545.7 m GM/SS-086 - Beinn Ruadh, 159.4 m GM/SS-090 - Beinn Dubh, 155.6 m GM/SS-106 - Cauldcleuch Head, 183.7 m GM/SS-131 - Hods Hill, 210.2 m GM/SS-178 - Craignell, 162.0 m GM/SS-230 - The Slate, 155.0 m GM/WS-051 - The Saddle, 211.7 m GM/WS-053 - Maoile Lunndaidh, 639.6 m GM/WS-106 - The Fara, 151.8 m GM/WS-233 - Carn Breac, 165.2 m GM/WS-260 - Beinn na Feusaige, 299.2 m
Lesson learnt, if I see any association update, update the GPX file.
None. Checking such things is part of the process. Where the new / old AZs do not overlap we raise a new ref and retire the old one. As you have noticed sometimes a new ref is not necessary even for a significant move.
None of the old summit locations were outside of the AZ as updated, for summits which did not receive a new ref. As to exact GPX way-marker locations, as outlined they may have been subject to reduced accuracy owing to the conversion process from NGR (with inherent 100-m resolution - as you can see from your histogram most sit nicely in the 0-to-100-m range). Nevertheless the actual summit locations would have been easily identifiable (e.g. keep at the top of the cliff / don’t go for a swim). RHoB provide lat/lon nowadays, as per GNSS results†, so there is no conversion process and you should be pretty safe to target the coordinates blindly. Of course I am speaking figuratively! Caution near cliffs is recommended.
Old and new locations of GM/SI-205 with the activation zone:
As you can see the old summit location (as per our working files - can’t comment on GPX) were/are both in the AZ (this is taken from OS Terrain5 DTM). It’s actually a fairly close call, with RHoB recording a 20-m drop to the col. I’m not sure why we didn’t update the name to “Sron an Duin” though.
[† Where RHoB have made a GNSS survey, which is still not everywhere I think. But whatever they have we have kept full resolution in GM.]