We’ve had a few questions recently about benchmarks and trig pillars and what they are and how they differ, so we thought we’d clear it up.
Most weeks we’ll see a Twitter conversation where someone is asking what this mark is:
A #TBT to the OS benchmark, spotted here by @770.92. These survey marks can still be found on walls and buildings across Britain and were a way of recording height. Today, our surveyors use GNSS technology and it takes just seconds to do a task which could take days in our past. There are around 500,000 benchmarks in various formats – have you ever spotted one?
Many think it is War Office-related, but it is in fact an OS benchmark (BM) and a means of marking a height above sea level. Surveyors in our history made these marks to record height above Ordnance Datum Newlyn (ODN – mean sea level determined at Newlyn in Cornwall). If the exact height of one BM was known, the exact height of the next could be found by measuring the difference in heights, through a process of spirit levelling. They can be found cut into houses, churches, bridges and many other structures. There are hundreds of thousands of them dotted across Great Britain, although we no longer use them today.
We usually share stories about our teams adding new features to the map, such as the Queensferry Crossing or even a whale, but we also have to remove features from our database. London-based surveyor Tony Killilea was recently tasked with removing a football stadium from the map…
With over 500 million geospatial features across Great Britain and some 10,000 changes taking place in the database each day, it’s not difficult to understand how our surveying teams are kept busy. From new roads to new shopping centres, it’s easy to forget about the existing features that have to be removed for new developments to be built.
The Queensferry Crossing opens to traffic today and joins the Forth Road Bridge and Forth Bridge in spanning the Firth of Forth. Our surveyors Derek Smith and Guy Rodger visited the site last week to add some final details, along with Alastair Dalton from The Scotsman newspaper.
OS MasterMap showing the three bridges
Opening tomorrow, during National Parks Week 2017, is The Sill National Landscape Discovery Centre in Northumberland National Park. Our surveyor Richard Bennett was on site recently to ensure the building was added to the map.
The Sill is the result of a partnership between the National Park and YHA England and Wales, including space for exhibitions, a café, a Youth Hostel, a rural business hub, and a shop specialising in local crafts and produce.
Richard was on hand to measure every aspect of the site and add the featured to 550 million in our geospatial database. His GNSS receiver locks on to several satellites and a series of ground stations (that’s right, no trig pillars required!) and the calculations are accurate to within a few centimetres.
A stunning development of new beach huts on the south coast has been added to our geospatial database ahead of the summer season.
The development, in Milford on Sea, replaces the old beach huts which were damaged and destroyed during a fierce storm on 14 February 2014. With building work on 119 beach huts and the surrounding area reaching a conclusion, it provided the ideal opportunity for our surveyor Joanne Lanham to officially capture and map the changes on the site.
We often share the photos taken by our Flying Unit in between their surveying tasks. And you’ll have seen the aerial imagery they take when surveying from the skies. But have you ever wondered what it’s like to do your daily work in the back of a Cessna 404? Roger Nock, one of our Flying Unit, took a photo of his workspace. Take a look.
Roger explained what we can see…
Update: DVD released on 24 July 2017. We have one copy of the DVD to give away. Just retweet this message by 12 noon on Friday 28 July: https://twitter.com/OrdnanceSurvey/status/889486114536476674
March 24 sees the UK film release of Lost City of Z. It chronicles the South American adventures of British explorer, cartographer and archaeologist Lt Colonel Percy Fawcett. I joined a panel discussion in London last week, along with historian Dan Snow and Lost City of Z author David Grann, discussing how Percy would have explored and mapped a new land. Catch up on the podcast here.
A member of the Royal Geographical Society (RGS), Percy Fawcett first arrived in South American in 1906 to survey and map an area of jungle lying on the Brazil and Bolivian border. The border between the two countries was not fully mapped and it was agreed that an RGS survey and map would be accepted as an impartial representation of the border. Today we would complete this activity using satellite systems and sophisticated surveying technology, which obviously wasn’t available back then. So, how would Percy and his team have gone about making maps?
It’s not every day that we add a whale to our maps, but surveyor Shaun McGrath did recently…
I first became aware of the Colonsay Whale some time after a visit to the Isle of Colonsay in the Inner Hebrides last year, on a particularly fine day trip to carry out some survey work. It’s a long day as the ferry sets off around 9.30 am from Islay where I was working on detached duty and returns around 7.30 pm. I had plenty of time to get the survey work done and it left me a little spare time to explore the island’s fine sandy beaches before the return ferry. I visited Kiloran Bay in the north, as recommended by the occupants of a house I had surveyed earlier that day. They also said that there was an even finer beach further north, but it was only accessible by foot and would have added a couple of hours to my trip – and made me miss the ferry.
Our surveyors are usually local to the areas they survey and this was the case for Andy Caulfield when he was mapping the new Tadcaster Bridge. The bridge partially collapsed in the aftermath of the Boxing Day storms in 2015, impacting local residents and businesses for the next 14 months while repairs were carried out. Many, like Andy, will have seen an 11-mile detour added to their days and are welcoming the reopening of the bridge.
Over the last few months we’ve been sharing unusual surveying stories with you – from mapping chalk figures to lifeboat stations to the aftermath of a flood. All of these tasks form a part of the 10,000 changes a day taking place in our geospatial database of Great Britain. The variety of jobs faced by our 250+ surveyors is unending. Take a look at these three examples:
Escape to the countryside