After an update announced on Monday 21 November, the number of summits on the Grahams list has increased from 219 to 231. The addition of 12 new hills comes as a result of a major revision to the qualifying criteria by list owner Alan Dawson, with a switch from Imperial to metric height.

The revision has met with a mixed reaction on social media from walkers currently working through the Grahams, as well as those who've already completed a pre-change round.

In a change presented as the definitive last word, 30 years after the classification was originally conceived, Grahams are now defined as Scottish hills between 600m and 762m in height, with a prominence of 150m.

While the lower height threshold has been rounded down from its previous 609.6m (2000ft) to a neater metric 600m, the upper ceiling of 762m (a straight translation of 2500ft) remains the same. Going metric brings the list into line with others Dawson owns/manages, the Marilyns and the SIMMs, and while it creates something of a measurement clash with the SMC's non-metric Corbetts and Munros, the upper limit of Grahams does still seamlessly connect with the lower end of Corbetts.

Between 1995 and 2014 the number of Grahams remained at 224. After subsequent height surveys of borderline cases, the tally settled on 219. However, these surveys had revealed that a lot of OS data for such lower hills was inexact.;

"It was clear from these results that spot heights on OS maps that had been derived from aerial surveys (taking photographs from planes) could not be relied on to produce an accurate list of hills" writes Alan Dawson in Ten Tables of Grahams: The Official List.

"The heights of trig pillars were correct, but the pillars were not always on the highest point of a hill."

In following years he set about the huge task of surveying the other hills, with help from Jon Metcalf who was doing a postgrad course in topographic science in Glasgow. Towards the end of that process, Alan began to conclude that making a switch to metric made sense.

"It was the landscape that jolted my thinking" he told us.

"[Before the change] I had to survey Cruach nam Miseag and Cruach Neuran as they are both 607m on the map, so there was a slight chance they could be 609.6. After all, nearby Cnoc Coinnich turned out to be 2.5m higher than the map height.

"The map was correct for both, but I was struck by how similar they are in character to the nearby Grahams of similar height, e.g. Cruach nam Mult and Cruach nan Capull. So they made 609.6m seem such an arbitrary and inappropriate cut-off point. And of course I knew about the three 609m hills that were Grahams until 2014. The 600m limit was appealing in its own right, so it all seemed an obvious and overdue change. In the High Hills book I tried not to be limited by round numbers, but if they make sense from a topographic perspective then I am very happy to use them."

In the new metric list, heights are given to the nearest 10cm, a level of precision that he is confident in thanks to the use of GNSS (Global Navigation Satellite System), which is usually accurate to within 5cm (if there is no large cairn obscuring ground level on the summit).

The drop figure, meanwhile, refers to the height difference between the summit and the relevant col.

"All the critical cols have been surveyed for hills with a drop of from 145 to 154 metres" writes Alan "so there is very little chance of any further changes to the list."

The 12 new summits are:

1. Hecla (S.Uist)
2. Ben Aslak (Skye)
3. Sithean Mor (W.Highlands south)
4. Burach (W.Highlands south)
5. Beinn a' Chuirn (W.Highlands south)
6. Ladylea Hill (E.Highlands)
7. Corwharn (E.Highlands)
8. Leagag (Central Highlands)
9. Sgorach Mor (S.Highlands west)
10. Cruach nam Miseag (S.Highlands west)
11. Cruach Neuran (S.Highlands west)
12. Well Hill (S.Scotland)

"These are all good hills" Alan tells us "with the possible exception of Burach. They include some superb ones, so the additions make the list more satisfying from a hill walking perspective as well as numerically. Pity that The Coyles of Muick is (are?) only 599.2m but you can't win them all and none of the other hills just below 600m have as much appeal as the additions." 

The newly extended list will give many keen Graham baggers new hills to climb. However, Alan Dawson is keen to stress that no one 'has' to:

"Anyone who has climbed the [previous] 219 Grahams is still a Grahamist and that will never change" he wrote on Facebook.

"This continues a longstanding principle that you do what is current at the time, as with the Munros before and after 1997. Whether anyone chooses to climb more hills is a personal choice."

For some, mopping up the new additions will be a pleasure, not a chore.

In height terms it's a lesser list than Munros or Corbetts, but connoisseurs of the Grahams tend to be attracted by the wilder and quieter qualities of many of the summits.

"These hills occupy a specific niche in the Scottish landscape" writes Dawson in Ten Tables of Grahams.

"They are not high or low, they are medium-sized, on average about halfway in height between sea level and the summit of Ben Nevis. They vary widely in appearance, accessibility and location..."

The Grahams are named in memory of Fiona Torbet (née Graham), who produced her own list of 2000-2500ft hills soon after Alan Dawson's book The Relative Hills of Britain was published. To keep things neat the two compilers met and agreed to amalgamate their lists.

"In July 1993, Fiona Torbet was unlawfully killed while on a hill walking holiday in the Western Highlands" writes Alan.

"In the aftermath of this terrible event, it seemed important to uphold the verbal agreement and retain the name Grahams for the hill list."

• You can add Grahams to your UKHillwalking logbook via the Grahams list here
• Published by Pedantic Press Books, Alan Dawson's Ten Tables of Grahams: The Official List is available as a printed booklet, or a free download here.