Formative yearsIts purple or orange-covered maps may be the favourites of peace-loving ramblers, but, like so many British institutions, the OS has its roots in war.
Although the first survey of the British Isles (the Principal Triangulation) was begun in 1783 by William Roy, the OS itself was formed in 1791 because of the threat of invasion by the French.
The government instructed the Board of Ordnance - the defence ministry of its day - to survey the south coast in preparation for any such onslaught.
The Tricolour never was hoisted in triumph over Kent, but the resulting maps became firm favourites with everyone from the military to the landed gentry, for whom the OS's unprecedented accuracy came in very handy when settling boundary disputes.
Surveying the country by hand was a huge task - although the first one inch to one mile map was published in 1801, the series wasn't completed until 90 years later.
In the 1930s, the National Grid reference system was established and the country was resurveyed using more accurate techniques. This resulted in the construction of 6,500 concrete trig points, many of them still standing today.
From the 1970s the 1:25,000 and 1:50,000 Explorer and Landranger maps were introduced, as well as a growing range of customised commercial mapping products at a wide range of scales.
In 1995, the OS completed the digitisation of some 230,000 maps, making the UK one of the first countries to finish such a large programme of electronic mapping.
Although it still sells 2.5 million paper maps a year, some predict their end is in sight. So watch out for outdoorsy types prodding at iPads in those waterproof pouches.
Since 1999, the OS has been a trading fund within DBIS, so it has to work for a living, selling geographic information for everything from satnav systems to healthcare providers, insurance to logistics.
However, along with the Royal Mail and the Met Office, the OS has been earmarked as a privatisation target. So it could end up in the hands of Capita or Serco.
The secret formulaBased in Southampton under chief executive Vanessa Lawrence, the OS has some 1,100 staff producing maps that are regarded as some of the clearest and most accurate in the world. Just try using an Italian map if you don't believe it.
And despite the fact that modern maps are drawn on computer using GPS data, teams of OS experts still set out, theodolites in hand, to survey the remoter parts that high technology cannot reach.
Don't mention ...Google, Apple et al. Winning on the internet calls for global standards and the OS is avowedly local - it doesn't even cover Northern Ireland.
*All figures full year 2012