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Great Britain’s tallest mountain is taller

18 Mar 2016
Ordnance Survey
Using GI and maps
ben nevissurveying

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.

Ordnance Survey
By Ordnance Survey
Press Office

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