Ordnance Survey: Putting GIS on the map

Ordnance Survey started mapping Great Britain in 1791. Two centuries on, the information its maps contain has swollen to fill a terabyte database, and new layers are enabling a whole new world of GIS applications

The surface of the Earth is, with one exception, one of the lesser-mapped places in the solar system. Both Venus and our own moon have famously been mapped more exhaustively than our own planet. The one place on the Earth that has been well mapped is Great Britain, thanks mainly to the paranoia of an 18th century government that wanted to plan adequate defences to repel invasions.

It is inconceivable that the people who began the job in 1791 could have any idea that, over two centuries later, the work would still be continuing. In fact, what began in 1791 as a finite job mapping the south coast of England to help plan defences against invasion, today spans the whole of England, Scotland and Wales, with over £100bn of commerce depending on it. Geographical data finds its way into some aspect of pretty much every company in the UK: Ordnance Survey, which today continues the job it started when it was the board of Ordnance -- the defence ministry of the day -- in 1791, believes that some 80 percent of all information includes some geographical element.

"Tesco uses geographical information to figure out not just where to put stores, but how to stock them," says Ordnance Survey marketing manager Neil Wilkins. "They need to know how to stock various stores depending on the local demographics."

Mapping the country to support such data is a job that will never finish. The current workforce at Ordnance Survey dedicated to mapping comprises more than 400 surveyors, who constantly measure and record the changing British landscape from a network of offices stretching from Inverness to Truro.

Information gathered by the ground staff is supplemented by an intensive programme of aerial photography, particularly in rural areas, resulting in about 5,000 changes being made every day to the MasterMap: to date there are some 400 million individual features.

Up until the 1970s, these maps were all paper-based: that meant a library of 230,000 sheets of paper, or tiles. Obviously, as the demand for mapping data increased, this situation proved increasingly inadequate, and so Ordnance Survey began a programme of computerisation. Even that job took almost a quarter of a century, and was not completed until 1995. But the effort was felt to be worthwhile: today, it means that extracts of the latest edition, which contains some 400 million features, can be accessed instantly by the public through a national network of computer-linked retail outlets in the Ordnance Survey Options network.

The live map can also be accessed by companies who want to build or implement their own geographical information systems. Significant features such as houses usually appear on the map within six months, says Neil Wilkins. A lot of work is done by the surveyors on the ground, and depends on building relationships with local authorities and the Land Registry. "We think we get about 80 percent of the information from these sources," says Wilkins.

The result is that everything larger than eight square metres ends up on the map, and lots more that is smaller. Measurements are accurate to the centimetre, claims Wilkins.

Ordnance Survey's MasterMap is also about more than just lines. When computerisation of the records began, OS maps were nothing but lines -- walls, ditches, hedgerows -- dividing spaces. Today the Master Map is all about what fills those spaces, and as a result is believed to be one of the largest Oracle spatial databases in the country, occupying a terabyte of storage space.

Information in this database includes everything from forests, roads and houses to garden plots and even pillar boxes and post codes. It is the post code data that lets the ZDNet UK/OS Wi-Fi hot spot map locate hot spots, for instance (the map is based on the MasterMap).

New layers of information are being added too, such as aerial photographic images that precisely match the mapping; data providing the addresses of all properties; and integrated transport information.

The new layers were launched in response to growing demand from mobile network operators, solution providers and software developers for flexible, high quality, consistent imagery mapping and integrated transport network (ITN) information throughout Great Britain. The first release of the ITN layer comprises Roads Network and Road Routing Information themes: The Roads Network theme features four million links that interact with the 400 million features of OS MasterMap, each link representing the precise alignment of every road in Britain and including digital information on the type and nature of each stretch of road.

Road Routing Information includes additional information on bridge height and vehicle restrictions, traffic calming, one-way roads and essential information about each junction.

Created from aerial photography, the Imagery Layer will provide a detailed and comprehensive aerial map of Great Britain. All images will be orthorectified -- correcting the positional and geometric distortions that arise both through the camera's position relative to points on the ground and through variations in height on the ground surface.

It is additions such as the ITN layer that have enabled Ordnance Survey to build some interesting proof-of-concept applications. One, using route-planning software hosted on servers for access by smartphone or GPRS-enabled PDA users, can track a driver's progress as they, for instance, head in to London for a meeting. "You can add traffic alerts to the route planner," says Wilkins, "and if there's a delay the system will automatically generate an email saying you'll be X minutes late, calculated on the state of the traffic and the quickest alternative route."

As the driver enters the central London congestion charging zone, the system can detect this and pay the charge by SMS. By tapping into the spatial data within the MasterMap, it can then give a selection of car parks and, could in theory pay the car park ticket. "If the meeting overruns, the system could be set up to suggest local restaurants -- there would even be opportunities to view the menu over your mobile phone," says Wilkins. "We've been spending a lot of time showing operators some of the types of applications that are possible with the latest MasterMap functionality. We see a lot of mileage in this."