Why GPS?

Scotland has magnificent but potentially dangerous country, and GPS can be a valuable aid to map reading under adverse conditions.

Source of GPS data

Grid References are usually given to 6 figures, in which a point is in a 100 m x 100 m square identified by the SW corner co-ordinates. This figure, accurate to 100 m, is usually sufficiently precise to locate the summit cairn even in mist. However, GPS wants 10 figure Grid References, i.e. the point is located in a 1 m x 1 m square. For the initial tables, I added 40 m to both eastings and northings on the basis that the co-ordinates of the NE corner might be used if the point was within 10 m of that corner.

Format of GPS data

Numbering system: I have changed section numbers to letters, adding leading zeros for sequence numbers 1 to 9 in each section, and adding the suffix T for tops. The description is a name condensed to 16 characters. Thus:

A01 is Section 1 No 1 Ben Lomond

A16T B A CH: W TOP is Section 1 No 16 Beinn a' Chroin: W top (i.e. a top)

The listing has been adjusted for recently promoted tops. The Symbol on a Garmin GPS 12 is a flag for a Munro, T in circle for a top, a wrecked ship for a demoted top.

The condensed names were derived without close regard to consistency of abbreviation, and in ignorance of Gaelic etymology; they are intended to be identifiable in a list for a section. How do you reduce a name like Mullach Coire Mhic Fhearchair, or the associated top Mullach Coire Mhic Fhearchair, Sgurr Dubh to 16 characters, limited to upper case letters, spaces, hyphens and numbers? Generally, Ben or Beinn become B or Bn, Coire becomes C, Meall becomes M, Sgurr becomes SG, Sron SR and Stob ST. The north west top may appear as NW TOP, NW TP or NW T (depending on the number of characters left). Apostrophes have been replaced by hyphens. If anyone is offended by the abbreviations, apologies; if you wish to make a more consistent listing of the names, let me know. As it stands, the list should be adequate as a working list on the basis that the SMC tables give L01 (on my numbering scheme) as Carn nan Gobhar, 992 m and L11 as Carn nan Gobhar, 992 m - the only difference is the grid reference. I am planning to work through the listings to use the numbering of the 1997 tables when time permits.

Tops are included for completeness; whether or not you are 'picking them off' or visiting them as part of a walking expedition; you often go over or near a Top to the main summit. Thus they can be used as waypoints on the route. The Tops are based on those listed in the 1990 and 1998 tables; it is planned to keep the 15 that were recently demoted (such as Sgurr Dearg, reduced to a mere waypoint on the way to the Inaccessible Pinnacle), but with a new symbol, a wrecked ship and suffix X. The 1998 SMC Journal cites a new Top, Knight's Peak, which I have added (plus a further 8 new tops). The Corbetts, follow the same numbering scheme with suffix C and a deer symbol. The Grahams will get the suffix G and the Donalds the suffix D, identified with an anchor symbol.

Of course, the total of 517 summits is too many for a memory of 500 waypoints. Editing the file to produce a new file with a sub-set of the Munros and Tops for the area you are visiting is quite easy with the selected numbering system. This numbering scheme also avoids confusion with automatically created Garmin numbers. In principle, you could load waypoint to your GPS directly, but that is really tedious (OK for one or two intermediate points you might identify on the day, but prone to error on the day, and just imagine entering the 17 Mamores Munros and Tops). This way you can delete the lot with impunity for some other purpose and reload the Munros when they are wanted again.

Using GPS

See write-up

News as of 2nd May 2000
GPS data before that date is less reliable than newer data

Apparently Selective Availability has been turned off, pretty much for good.
I put my GPS outside for half an hour and recorded ranges of 6 to 8 metres on OS northings and eastings, rather than the previous 200 to 300 metre range, consistent with SA having been turned off (but note it may be turned on again in the event of a 'serious' conflict). If SA has been turned off, there is scope for more accurate GPS waypoints being determined for Munros, based on 'on the ground' measurements. If only I could volunteer!

HELP PLEASE (Posted on SMC bulletin board)

With Selective Availability switched on, there was no advantage in being more precise: readings were no more accurate then +/- 200 metres.

Now that GPS is free from deliberate error, readings accurate to (say) 10 metres will be routine. It's worth thinking about collecting Munro data using GPS. There are two distinct data sets I propose: (a) Munros and Tops to 5m (rather than the 100 m of standard OS grid references) (plus Corbetts, Grahams and Donalds) and (b) key waypoints on the route up and (probably more important) the safety route down. I was particularly taken by the fact that altitude readings actually have a meaning.

Munros and Tops:
At the summit, get a time averaged reading of the summit location, with altitude which may have to be recorded manually (now altitude readings are consistent, but is there an inherent displacement?). Put the GPS on the summit cairn, mark the point averaging the data for a few minutes, until the FOM (Figure of Merit) has dropped to less than 5 m. The FOM figure and the altitude given by the GPS should be recorded as well as the name of the Munro/Top.

GPS waypoints for deleted Munros and Tops, Corbetts, Grahams and Donalds also accepted!

Routes:
GPS data on routes should be seen as back-up to navigation with a map and not a substitute. The first priority is to provide data to lead walkers to a safe route from the summit, i.e. the route to the top of the descent(s) from the summit plateau. It is also useful to identify where the summit path leaves the valley path, often identified by a (missable) cairn. Typically, routes would give the car park (or the point the route leave the public road) so that I can see where you are starting from, with key junctions, the top of the main ascent to the summit plateau, the summit itself (with time averaged GPS data as above) plus tops and the point the route leaves the summit plateau. The data should allow forward and reverse routes (hence the point at the top of the ascent for straight up and down outings rather than traverses of the mountain). These should be specified as waypoints, not just points on routes (which give truncated waypoint data) or tracking data (difficult to identify key points, but useful for checking the distance walked - and interesting if you select a fixed time interval of, say, 4 min, when you look at a graph plot). A written description would be useful.

I do not want to generate routes that can be followed 'blind', without reference to a map, but rather to provide safety information as back up.

Please e-mail me ( Henry Marston with attached text files of waypoint and routes and relevant information (background to route e.g. as described in SMC Munros book, altitude of summits as recorded by GPS if not included in downloaded data file), GPS unit (e.g. Garmin 12), and download software package (e.g. PCX5). Make sure you have set Ordnance Survey GB as the map datum and the British OS Grid as the Grid option.