The official increase, which is not the result of a geological movement, was discovered following the restoration of the trig pillar on Ben Nevis, when OS took the opportunity to re-measure the mountain. The change in height is down to the technology OS now uses to survey and measure giving greater accuracy than when Ben Nevis was last surveyed in 1949.
Back then it took a team of seven surveyors 20 nights to obtain their calculation. The new measurement was achieved by positioning a geodetic survey grade GPS receiver at the summit of Ben Nevis for two hours of constant data communication with satellites orbiting the earth. Data was taken back to OS head office for vigorous rechecking, before the new measurement was confirmed.
Mark Greaves, Ordnance SurveyÂs Geodetic Consultant, was the first person to discover Ben Nevis had grown. He says of the experience: ÂThe 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 thatÂs why Ben Nevis will now be officially known as 1,345m.Â
Field Surveyor Angus Hemmings was one of three surveyors who climbed Ben Nevis to take a new measurement. He says: ÂWe were asked to check if the recent repair work to the cairn had affected the position of the trig pillar, and this provided us with a sensible opportunity to resurvey the summit.
ÂIt was raining, sleeting and snowing at the summit, but harsh weather doesnÂt affect our equipment or readings. What it did do though, was give me a greater sense of respect for the 1949 surveyors. Each day they hauled 200lbs of equipment up Ben Nevis and its surrounding mountains. They also had to wait till night, because strong lights were shone from the trig pillars of the other mountains onto Ben NevisÂ, which enabled them to collect their data.
ÂIt 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.Â
OS maintains up-to date-maps for the entire country, holding up to 460 million geographic features in its database of Great Britain. Over 10,000 changes take place each day in what is thought to be the largest geospatial database of its kind in the world, providing valuable information to government, business and citizens.
The new height for Ben Nevis will be seen on OS paper maps, starting with the OS Landranger map series. Users of OSÂ digital map service, OS Maps, will be able to see the new height on OS Landranger and OS Explorer maps immediately, as updates in the geospatial database can feed across multiple digital products.
OS expertise now expands across 3D, Virtual Reality app development, including a virtual tour of Ben Nevis released last year, GIS solutions and a host of business and consumer digital products.
OS Marketing Director, Nick Giles, says: ÂThis year OS celebrates 225 years of delivering the most accurate portrait of Great Britain. It is a testament to the data collecting skill of all our surveyors, not just those hardy seven measuring Ben Nevis back in 1949, and the constant emergence of new surveying technology, that OS is able to make such a claim. In reclassifying the height of Ben Nevis our map becomes even more precise. Now itÂs officially taller, I wonder how many will feel tempted to revisit its summit.Â
OS always recommends taking a paper map and compass when adventuring in rural and remote areas; and being equipped and knowledgeable about mountain environments.
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