Image caption Dave Wareham's margin of error is no more than 2.6cm

At the main 2012 Olympics site in east London, Dave Wareham has a white hard-hat perched on his head as he stares at the screen of his chunky laptop.

Under a low, grey sky, drizzle mists the site, while dozens of lorries and an endless stream of cars of varying sizes pootle about under severely restrictive speed limits of as little as 5mph.

These vehicles are transporting the 10,000 or so fellow hard-hatted workers who still have much to do to make the site ready for the 2012 event.

The builders' plans are well-made, as indeed they need to be. But for spectators, security staff and emergency services - let alone the athletes - navigating the site will not be possible without one thing: a map.

And that is what Dave Wareham is setting about making for the Ordnance Survey (OS).

Streets have no name

The OS is charged by the government with recording every physical element of Great Britain (Northern Ireland has its own organisation, OSNI) - and this may be its biggest job yet.

"Our aim is to accurately place something within a maximum tolerance of 2.6cm," says Mr Wareham.

"Certain things we already know about on the site - others are more vague. The main arena, for example - although the outside is built, the shape of the inside is not fully there, so there's no point us looking at that until it is finished."

Image caption The road with no name will end up on an OS map - once it has one

The way it works is this: Dave stands in a spot with his laptop and his GPS receiving rod, which speaks to between four and seven satellites overhead, which give his position within two to three metres.

Then, in his backpack, there is a mobile phone that sends the same information to some 100 OS ground stations all over the country - they are accurate to a couple of centimetres.

They report back and confirm, or correct, the location that Dave is telling them about.

There is a great deal of that to be done at the Olympic site.

In fact, the site is still such a work in progress, one road has not yet been named - it is simply called White Space Avenue.

Historic role

The OS measures the complexity of its job in what it calls "units of change" and has a target of recording 96% of all major changes made in the country within six months.

But this one, says Mr Wareham, is the most complex in terms of the number and scale of new buildings, roads and other physical elements that are springing up at the Olympic site.

Image caption OS maps sell three million copies a year, despite online availability

The Athletes' Village alone is 11 blocks containing 3,300 dwellings. That, says the OS, makes it the largest and fastest-built domestic development of the past 40 years.

The organisation began the job of charting the country more than 250 years ago. Its first big endeavour was to map Scotland after the battle of Culloden.

Then in 1791, in the face of political turmoil in France, the Board of Ordnance, which supplied armaments to the army and navy, was ordered to map the south coast of England in order to be prepared for any invasion.

The Ordnance Survey was born - and in the intervening years, it has moved from munitions to the more mundane.

Valuable information

Today, Ordnance Survey is not only a civilian outfit, it is a state-owned trading company with 1,300 employees and a strong commercial flavour.

Its last declared profit was £16.6m, a return on revenue of 14.5%, although one-off restructuring costs for the 2009-10 year put a big dent in that.

OS in highlights 1746: First survey - of Scotland after battle of Culloden

1791: Threat of Napoleonic invasion means Ordnance Board starts mapping England

1801: First map published - of the county of Kent

1899: Boer War means OS maps South Africa

1918: 32 million maps made for First World War

1920: First tourist map - of Snowdon

1945: 342 million maps for WW2

2001: MasterMap - UK's first updateable digital database

The information gathered by Mr Wareham and the other 300 OS surveyors around the country has a keen constituency of customers.

MasterMap, the UK's first comprehensive digital updateable database, contains 440 million features - from lamp-posts to post boxes.

Places such as these, which have no postal address, still need to be logged, says the OS.

Paul Beauchamp from the OS points out: "The emergency services need to know where everything is. It may not have a mail box but it does need to be found."

The OS sells this information to all kinds of bodies, such as utility companies and local authorities.

Cardiff Council, for example, has saved more than £2m since it used OS data in 2008 to reorganise its school bus network.

As a result, the distance covered was reduced by 1,200 miles each day, meaning 40 fewer buses are now needed.

Don't blame us

Water companies also use OS information, for example, during floods, to check where the water tankers are and get them to those areas most in need.

Image caption The Olympics site at Stratford East London 2006 (left) and 2010 (right) - all changes must be mapped

A key source of revenue has come from satellite navigation systems. OS sells its information directly to Garmin, while other firms, such as TomTom, base the information on OS data but produce their own algorithm for their routing information.

Mr Beauchamp says: "Although we sell the underlying data to the vast majority of sat-nav systems, we don't do the routing for all of them."

Basically, he is saying, don't blame us.

Of course, the most visible branded items are still its maps. Profits from these still account for 8% of its business, despite the fact that the information is easily accessed through the internet.

The best-selling Explorer Orange label maps, loved by walkers and cyclists for their clarity of appearance and accuracy of information, account for the lion's share of the three million copies sold each year.

Mistake?

Each one produced is underpinned by meticulous exploration of every tangible aspect of any part of the country - be it a field, a cow barn or a public toilet.

Sport, news and more 2012 information BBC London 2012

These paper maps are revised every three to four years.

Back at the Olympics, Dave Wareham is still beaming back his position to the OS base in Southampton, via 100 or so satellites, accurate to within 2.6cm.

I ask him if he ever makes mistakes and - if so - what his worst one had been. He looks grave.

"Oh yes. There was one time I was measuring a house - one of three - I relied on earlier data and failed to check it.

"It ended up half a metre out."