Definitions, Explanations, & References

(continual work in progress in the quest for comprehensible English)

Abbreviations | Area | Col | "e" | Grid-ref | Height | Hill name | Island | Maps | Prominence | References | Saddlepoint | Triplepoint | Watershed

Abbreviations:  as used on this page and throughout

1 foot = 0.3048 metres precisely.
Irish [Republic] Ordnance Survey.
metres.  1 metre = ¹/0.3048 feet, precisely, or approximately 3.280840 feet.
Ordnance Survey -- either a general term to cover all the respective bodies in the Isles, and/or a reference to THE Ordnance Survey (as it was then) when it was responsible for mapping all these Isles up until Irish independence.
Ordnance Survey of Great Britain.
Ordnance Survey of Northern Ireland.
Scottish Mountaineering Council.

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The entries here refer to regions defined by other sources and are included as an aid to cross-referencing with those sources.  The numerical part refers to the Section headings in the publications of Dawson and Clements (see below).  With a letter added a Region within that section is defined.

The Section numbering has its origins in Munro's original tables of Scottish 3000ft mountains, (Sections 1-16 for the Highlands, 17 covering the isles of Skye and Mull) though 2-16 were renumbered by the SMC as of their major revision of Munro's Tables in 1974, when the boarders were also adjusted in some cases.  These SMC sections have since been expanded and added to by Dawson to cover the rest of Scotland (18-28) and Britain and, with Clements work on all Ireland, now cover the entire Isles from St Kilda, to Kent, to Kerry; from Shetland to the Scillys.

Section 29 covers the Isle of Man; 30-32 cover Wales; 33-42 England; 43-44 Northern Ireland; 45-56 the Irish Republic.  Most of the Sections are subdivided into smaller Regions -- see the relevant TACit publications for details.

I would prefer to carve up the Isles into areas with a contiguous watershed (and islands included accordingly with regard to how the watershed would extend when the tide goes way, way, out come the next ice age!), thus causing their boundaries to be river valleys and their interlinking cols, and indeed Sections 1-16 do follow such a pattern (intentionally or otherwise, I do not know), but beyond these the convenient boundary markers used by Dawson (especially roads and county boundaries) too often work against this.

They are nevertheless retained here to better aid reference to Dawson's and Clements' works, being as they are somewhat more extensive and detailed than mine.  In any case, the tables published here mostly include summits that are so distinct from each other that they often define the very ranges if not entire regions that they are in.

For an entirely different take on `Region', see Stewart Hinsley's similarly inspired (though tooth-itchingly error prone) tables, where a summit's region is defined as being the entire area for which that summit is the most prominent, i.e. has the greatest relative height.  Thus, Carrauntoohil gets all of Ireland, being its highest mountain, but Brandon Mountain, high and proud and second most prominent on Ireland though it is, can claim only the Dingle Peninsula on account of being too close to Carrauntoohil.  I only wish I'd thought of it first.

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Cols and saddlepoints:

A col is the name for the surface of a gap between two tops -- ideally that gap is a notch in a craggy ridge, or at least a pass linking two mountain ranges as you walk from one to the other (or from a driver's perspective, linking two valleys as you drive from one to the other).  Unfortunately, sometimes we have to make do with finding the lowest dip in a gently undulating marsh the size of a county.  It's still a col, broadly speaking.

Another term sometimes used is saddle, an aptly descriptive term bearing in mind how from the walker's and horse rider's perspective the col / saddle turns downwards at the sides and upwards in front and behind.

At most points on a hillside you are on a slope where you can readily imagine a contour line (i.e. a line that is continuously at the same height) running across the hill from your feet with the land rising above you on one side and falling away on the other.  Then there are summits, whether high or low, rounded or peaked, whose very definition is that land falls away from them on all sides (and you will occasionally find depressions, where the opposite holds true).  The saddlepoint, the crucial part of the col, is the precise point from where you can draw an `X' with you contour, in effect two contours kissing and parting, where the land may be split into four parts, alternately above, below, above, and below again the height of the saddlepoint.

It is the height of this point that we subtract from the appropriate summit's height to find the prominence figure for that summit.  It is often difficult to detect the location of the precise point on a col that is the true saddlepoint, (as it is, come to that, difficult on occasion to pin down a precise summit! -- e.g. Black Mountain on the Wales/ England border) though you can still work out its likely height to a fraction of a metre if you are at the col itself.

Note:  It is mathematically possible for a col/saddle to be the meeting point of three or more ridges (and an equal number of valleys between, of course) but it is very difficult to achieve in nature, though near misses can be found where two cols rest almost side by side, a few hundreds metres apart.

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What the heck is "e"?
It's a maths thing.

e = 2.718... (or 1 + 1/1 + 1/(1*2) + 1/(1*2*3) + 1/(1*2*3*4) + . . . and so on forever) and is one of those peculiar numbers, like pi (3.142... circumferences and diameters, and so much more) and Phi (1.618... "The Golden Ratio"; the ratio of your height against the distance from your belly button to your toes; the curve of a snail shell; Fibonacci numbers; etc), that appear all over the place in mathematics.  e takes starring roles in natural matters such as rates of decay and growth, and unnatural matters such as statistics.

Why do the tables end where they do?

As there is no minimum qualifying height for hills ranked by prominence, any tables here are just the top end of an infinite list . . . what you choose to aim for as a minimum depends on what's available to you in terms of time, distance and ability.  To bag all the hills of, say, 13.44 metres prominence seems an absurd target and probably is unless you're confined to, perhaps, Cambridgeshire.  A hill of 134.4 metres prominence would rank about 200th in Wales, but barely 2000th in Britain, whilst Ben Nevis itself at 1344 metres quite possibly doesn't rank in the top 1000 on a global scale.

You might choose to aim to bag the top 10, or 100, or 1000 in your chosen location (local hills, county of birth, country, continent, whatever).  Equally you might choose a limit based on the most prominent hill, and take half its prominence as a qualifying height, or maybe a tenth.  It's all arbitrary and, in any case, if you're the type to complete a list then once you have completed you're as likely to extend it anyway if you can't move targets and bag elsewhere.

672m prominence (i.e. 1344/2) gives a list of seventy-odd very distinct and worthy hills in Britain and Ireland -- a fine start, and perhaps all some of us will ever get around to doing given other commitments.  For those for whom peak-bagging is what they are committed to, 134.4m (one tenth of Ben Nevis) might barely keep you going until your dotage but certainly won't if you're a fell-runner.  A few people, even a few non-fell-runners, have nearly completed such a feat in Britain by bagging all but a handful of the Marilyns (prominence of 150m or more), the SubMarilyns (140-150m), as listed in Dawson's book, and sundry other high tops as found in other TACit publications.

I chose 1344m/e (or divide whatever is the maximum prominence of an area by e) because I am, or was, a mathematician, and e is the base of the natural logarithm, and logarithms are the basis of distributions, and it's the distribution of hills that gives us something to go and bag, so e seemed the natural choice.  (It's a maths thing.)  If I completed any given target, I'd tend to want to revise targets down and divide by e² instead.

. . . and then there is accounting for error, so depending on the data used to make the list, you'll want to bag everything with up to 10m less prominence, just in case (hence the tables go a little beyond their respective cut-off figures) -- you do want to be sure you're playing the game properly, don't you?

As for publishing the tables here, what appears is enough to give an indication of the variety of hills at the top end without impinging on more detailed work by others.  Besides, when you get TACit tables, you get Dave Hewitt's notes on the baggers themselves and their exploits -- which can be far more interesting than all this numerical data.

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The usual six-figure grid-references are provided throughout for summits, though they may or may not be entirely accurate.  The local map should always be checked, and all suggested corrections will be duly considered.  In some cases hills will have more than one candidate for highest summit and the true bagger will always visit all potential claimants, just in case.

When grid-refs for cols are supplied here (as they will do in time) they shall be kept only to four-figures (i.e. a resolution of 1000m, or 1km) as they generally can't be pinpointed from use of maps alone.

Northern Ireland and the Republic of Ireland share a common grid which is entirely separate from that used by the OS(GB).  Note that IOS and OSNI grid-refs have a single letter prefix whilst the OS(GB) uses two letters.

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The height of each summit is given only in metres (never feet), and refers to the map height as usually published by the respective OS.  For heights made by ground survey at triangulation points the `maximum error' is ±;1m. , and is that much only due the necessity of rounding (where heights are published to one decimal place, the max error is ±0.7m); For heights calculated using aerial photography on the 1:10 000 scales it is ±3.3m.  By maximum error it is meant that 99.7% of all measurements are correct to this degree of accuracy, i.e. the OS use three standard random errors (plus systematic error) as their limit.

Note that sea-level, i.e. 0 metres, has different definitions across the Isles.  The Datum for all Ireland is at Malin Head, Co Donegal.  That for Britain is at Newlyn, Cornwall, though local datums have been used for some of the outlying islands in the past.

It should be noted that the height given for a triangulation pillar (or "trig-point") is that at its base.  When the trig-point has been placed on the very summit, it has been the practice of the OS to build this base at precisely the height of the formerly undisturbed summit height.

The following applies to OS(GB) only:
At times contrary information can be gleaned from different yet equally current OS publications.  There are various reasons for this that can be explained as follows:

TACit Tables (and friends) have the laudable policy of chasing down any and all such contradictions, getting definitive responses from the OS(GB) where possible (think:  `blood', `stone', though responses vary) and tables are updated accordingly.  The Significant Summits tables will be similarly updated (subject to me keeping up with news).  Alas, it should be noted that the OS(GB) have a habit of digging up old errors and contradictions as well as new ones with every new publication.

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Hill name:

The hill name as it appears on OS maps.  Note that the OS(GB) seem intent on a process of gaelicizing everything north of the Highland line, even names which are evidently Nordic in origin.

I will tend to use the name of the broader hill or mountain name rather than that of a specific summit, as the former is generally more broadly known, e.g. `Cadair Idris' in preference to `Penygadair'.  When at a loss, I defer to Dawson, et al.

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Given except for hills on the main islands of Britain and Ireland.  For quick reference between these two, check the grid-ref (always two letters for the British grid, always one for the Irish) or the Area code (43 and above for All Ireland).

In cases where the island name is not unique, this is further qualified by the island group or neighbouring larger island or region, e.g:  both Orkney and Shetland have a `Mainland'; there are several Holy Islands.

Where the hill is the island and shares its name, no separate entry is given.

For brevity, in the tables the prefix "Isle of" and suffix "Island" have tended to be left out, especially for larger islands, as is often the case in verbal usage.

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The maps listed contain the summit point -- your preferred route might well begin on or continue through other maps.

Map numbers with prefix `D' refer to the 1:50 000 Discovery and Discoverer series of the IOS and OSNI, respectively.  (Co-operatively, the map index-numbers compliment each other without duplication.)

Triple-digit map numbers refer to the 1:25 000 Explorer Maps of the OS(GB) -- the orange covered maps now extent in many stores.  As of April 2003 this range has just been completed to cover all Great Britain.

Map numbers with prefix `OL' refer to what until recently was the 1:25 000 Outdoor Leisure series of maps of the OS(GB).  These have now been incorporated [read:  fudged] into the Explorer series -- they bear a yellow flash on the orange cover and an OL prefix with the map number.

NOTE!!:  except for the rash of purple plague (the usage of a dark purple to highlight access areas that makes useful navigational features such as walls / fences hard to read) there is often very little new on the `new' Explorer and Explorer OL maps, so don't rush out to buy them without giving them a good browse first -- there'll be another edition of more use when the Right-to-Roam laws (the CRoW Act) take effect.

`IoM' refers to the Isle of Man.  The OS(GB) cover this with Landranger 95, but have not (yet?) included it in the Explorer series -- they do however appear to mention the Isle of Man and 1:25 000 mapping in the same sentence on their Getamap frontpage.

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Definition of prominence:
Prominence is the term used by baggers in America and mainland Europe for what is sometimes referred to in Britain variously as `minimum reascent', `relative height', and `drop'.  Here are a couple of attempted definitions to make this apparently awkward concept clear.  The prominence of a summit is:

For an expanded explanation, see this (im)practical example.

Note:  In the case of the prominence of the highest summit on an island, we take its map height as its prominence, i.e. Ben Nevis has a height and prominence of 1344m, and we don't worry about the submerged col to the mainland lurking on the sea bed under the Straits of Dover.

Accuracy of Prominence:
In Significant Summits tables, this figure is given to the nearest metre and then calculated to the nearest foot by dividing by 0.3048 (which is the precise figure as stipulated by the law in the United Kingdom -- not sure about the Irish Republic!, but the global scientific community concurred on the same figure long before it became law).  Where the value in feet might be one higher than that given in other tables, this is likely to where the other compiler has converted to feet by multiplying by 3.2808 . . . which is close but not exactly the same.

It should be noted in any case that although the figure is given to the nearest single metre, the accuracy of the prominence figure is subject to a `maximum error' of ±3.5m in the best case and as much as ±10m in the worst, depending on the methods of height measurement used for summit and col.

Note:  The range for `maximum error' is defined such that 997 times out of 1000 the true figure will be within the range given, technically [statistically] speaking this is defined by OS(GB) as three times the standard random error plus the systematic error (Harley, p164).

For the figures for hills in all Ireland I generally defer to Clements' work.  Irish maps rarely include spot heights for cols and thus most figures are estimates -- Clements chooses to estimate the prominence (oddly, as opposed to the col height) to the nearest 2m, or 5m when dealing with non-metric maps. In the latter case the prominence figure is qualified with a `c'.

We might just as well put a `c' to all figures -- even when the spot height apparently at a col is at its most accurate (and when taken from ground level surveys, usually on roads, that is very accurate indeed) we have no guarantee that the height given is for the saddlepoint.  Roads often do not pass through the bottom of a pass but on the hillside just above it as, for example, drainage is often poor at the col itself, and the figure given might not be for the high point of the road anyway.

Even less reliable are the spot heights generated by aerial photography (given in brown type on 1:25 000 maps) rather than by people at the scene on the ground (given in black type on 1:25 000 maps -- no distinction between the two is given on 1:50 000 maps).  In this case the col is far harder to discern and it is established OS(GB) policy to, where possible, pick any handy minor feature and give the height for that.  But you can rarely tell just from looking at the map what the spot height is fixed on.

(This can lead to unfortunate errors from the list makers, the most marked perhaps being everyone's assumption that Craiglwyn in the Carneddau (SH730608), height 623m, did not make the usual heightist criteria for Wales of 2000ft minimum height / 50ft minimum reascent as its nearby col had a spot height of 609m leaving Craiglwyn allegedly a metre short -- many were loathe to believe this, it being screamingly obvious that it was greater than this if you stood at the col itself, and indeed it turned out that the map-makers had chosen a column of rock to fix their spot height on (and had little or no opportunity indicate this) and the saddlepoint is in fact a mere 602m high.)

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Triplepoints & Watersheds:

Triplepoint is the term used to denote the precise point where a ridge divides in two, or alternatively where two or more ridges meet and proceed as a single one.  This point may or may not be a summit of note, or possibly not a summit at all but an otherwise nondescript shoulder.  The more significant triplepoints mark the places where three large river basins meet, such as the one near the site of the Battle of Naseby where the Trent, Thames, and Severn basins meet.

The chains of ridges separating such basins are known as watersheds, though the phrase is sometimes used to denote any series of ridges and interlinking cols even when they end at the confluence of two streams rather than the coast.

Other notable triplepoints are where two or more notable watersheds converge, such as where the Welsh watershed meets (near Keele) that running down the spine of England.

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Dawson, Alan  Relative Hills of Britain  (Cicerone)  1992.
Harley, J. B.  Ordnance Survey Maps -- a descriptive manual  (Ordnance Survey, Southampton)  1975.
TACit Press publications:
   The Hewitts and Marilyns of Wales  1997
   The Hewitts and Marilyns of England  1997
   The Grahams and New Donalds, 2nd Ed,  1999
   The Corbett Tops and Corbetteers  1999
lists compiled by Alan Dawson, and
   The Hewitts and Marilyns of Ireland  1997
compiled by E. D. Clements.

All TACit publications are available in booklet form from TACit Press, each for somewhat less than the price of a map.  These also contain much else in the form of useful notes and data about the hills themselves, and historical notes from Dave Hewitt (the series editor).  Details of major corrections are also published on line, at Dawson's own MARHOFN site, dedicated exclusively to Marilyns (hills in Britain with a relative height [prominence] of 150m) and Marilyn baggers.

Most of the data in the Significant Summits tables has been gleaned from maps published by the OS(GB), the OSNI, and the IOS.  It was then brushed up to conform with the high standards set by the TACit Tables as listed above though I have a few minor disagreements with Dawson's data.  These are either where his data is illogical (mostly where he appears to have lost track of cols separated from their summits by the odd hundred miles -- not least a rash of eighty- and ninety-something metre cols for the more prominent hills of the south and south-west), or where he has news of revised heights since published (or unpublished but admitted to by the OS after repeated questioning) and I have missed the news (or just as likely shuffled my notes).

In cases of doubt, I defer to Dawson's data, and you should take his word on it over mine unless indicated (and he is certainly aware of any disputes I have -- he has a fair few rabid enthusiasts out there giving news of new or incorrect data).

Much of the Irish data has been quoted from and/or derived via Clements' booklet and amendments subsequently published in The Angry Corrie.

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(Significant Summits)