Great Britain’s tallest mountain is taller

It’s not every day that our surveyors have the chance to climb Ben Nevis with all of their kit and resurvey the mountain. But they did recently and found that Great Britain’s tallest mountain is taller than we thought. Our new paper and digital maps will show the height as 1,345m and not 1,344m.

The latest Ben Nevis map

The latest Ben Nevis map showing the new height of 1345.

We took the chance to resurvey, and send our surveyors up a mountain, after the recent restoration of the trig pillar atop Ben Nevis. The increase isn’t down to geological movement, or the restoration of the trig pillar either. The mountain has ‘grown’ because the technology we use to survey today is more accurate than the kit used when Ben Nevis was last surveyed in 1949.

Back then it took a team of seven surveyors 20 nights to obtain their calculation using hundreds of pounds of kit hauled up the mountain. Today, three surveyors used a geodetic survey grade GPS receiver for two hours of constant data communication with satellites orbiting the earth. The team then took their data back to head office to be checked and confirmed.

Mark Greaves, our Geodetic Consultant, was the first person to discover Ben Nevis had grown. He says of the experience: “The new height relates to the highest natural point on the summit and was measured as 1344.527m. I double checked everything and asked others to do so too. What is amazing is how close the surveyors in 1949 were. The measured height has changed by centimetres, but those centimetres mean we now need to round up rather than down. So that’s why Ben Nevis will now be officially known as being 1,345m.”

Condition on Ben Nevis for the team

Conditions on Ben Nevis for the team

It was raining, sleeting and snowing at the summit when our team were there, but harsh weather doesn’t affect our equipment or readings. It was a very different experience back in 1949 when the teams hauled 200lbs of equipment up Ben Nevis and its surrounding mountains each day. They also had to wait till night to survey, because strong lights were shone from the trig pillars of the other mountains onto Ben Nevis’, to allow them to collect their data. It took the surveyors 20 nights because they only had three clear nights in that period to get it right. To do the best possible job it had to be run with military precision, everything they did had to be timed to perfection. Their effort and accuracy is remarkable.

The height of Ben Nevis is just one feature in our database of Great Britain that contains up to 500 million geographic features. The new height for Ben Nevis can be seen on our new OS Landranger paper maps and on our digital maps.

Safety is paramount when out exploring the mountains, we always recommend taking a paper map and compass when adventuring in rural and remote areas; and being fully equipped and knowledgeable about mountain environments.

Why are there brackets around the height of Ben Nevis?

Find out more about the work the team carried out, including how to measure a mountain, why there are two heights on the Ben Nevis map, and how the team carried out their work in 1949: www.os.uk/bennevis

See more Ben Nevis photos from the team on our Flickr page.

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10 Responses

  1. Gerry McGarry

    Looks like we will be climbing a wee bit higher when we have our geocaching event at the trig pillar in July. One of many of our geocaching events celebrating 80 years of OS trig pillars.

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  3. Jake

    Do you know what the precise value of the 1949 survey was (“the measured height has changed by centimetres”)?

    1. Hi Jake

      Great question, but sadly the exact value from 1949 hasn’t survived. On maps, you’ll see the figure of 1,345m replacing the former height of 1,344m. Our surveyors measured the highest natural point on the summit as 1344.527m, which has been rounded up to 1,345m. The records from the last survey in 1949 do not show the exact measurement taken, we only know the official rounded-up figure of 1,344m, which reflects the changes in surveying and recording data between 1949 and 2016.

      Thanks, Gemma

  4. Hello Gemma,
    Since reading about the rounding up of the height I too was interested to know what it was previously and I note Jake has already asked. Your response interested me as you say the 1949 height of 1,344m was not recorded in detail, but was rounded up. Which if correct (and I strongly presume it is) suggests that the old height must have been greater than 1,343.500m (otherwise it would have been rounded down).
    Would I be correct to assume that ?
    I ask because I want to crudely assess the relative accuracy of the height in metres versus feet. I think the rounding up/down will be a significant aspect of this.

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