Armchair explorers who soar over 3D cityscapes on their computer may be used to the idea of maps with an extra dimension. But they are now getting accurate enough to offer much more than a preview of your next holiday destination. Accurate, large-scale 3D maps could soon change the way we design, manage and relate to our urban environments.

"Everyone is now familiar with 3D maps, we're trying to take them beyond simple visualisation," says Glen Hart, head of research at the Ordnance Survey (OS), the UK government's mapping agency, based in Southampton.

As part of a project to demonstrate the potential of 3D mapping, the coastal resort of Bournemouth in southern England has probably become the best-mapped place on the planet, says Hart.

Lasers were fired at the town from the ground and from the air to capture the height of buildings, trees and other features, using a technique called Lidar.

Adding information from aerial photos and traditional surveys produced a full-colour 3D map, built up from more than 700 million points. The map is accurate to 4 centimetres in x, y and z - by comparison 3D structures in Google Earth are accurate to about 15 metres.

"It's almost what you'd see if you flew around the area," says Hart.

OS is not the only organisation to be exploiting improvements in the hardware and software needed to capture and model cities in 3D. Detailed digital 2D maps, like those the OS maintains of the UK, already underpin the everyday activities of businesses and governments the world over. They are annotated and overlaid with everything from the layout of electric cables to data on air pollution.

Companies are now building large-scale 3D maps to be used in the same way. "Now it's not just buildings, but floors within the building that could be annotated," says Hart. "Insurance companies, among others, might be interested to know which businesses work on which floor to assess flooding risk." The new generation of maps can capture details like mailboxes and lamp posts too small to appear in existing city-scale virtual maps.

Infoterra, a firm based in Leicester, UK, supplied 3D data used in Google Earth, and will launch its own 3D city-mapping service, Skape in January 2010. It also uses Lidar to capture the heights of buildings and other features, and uses aerial images taken from a low angle to provide surface detail at a spatial resolution as low as 4.5 centimetres.

"This is not just eye candy," says Infoterra spokesman Jamie Ritchie, "we have 3D maps of every building in England, with oblique imagery of urban centres."

People who design, build and live in urban areas will be the first to benefit from these new maps. "Professionals like architects can delete buildings from a high street and import their own designs into the urban landscape," Ritchie says.

Andrew Hudson-Smith at the Centre for Advanced Spatial Analysis (CASA), University College London, says such maps could even make town planning a more democratic process.

"I think it's fantastic - you could log in to get all of the local planning applications in one place, and then have a free and open say on the proposals," he says.

But these highly realistic 3D urban models do more than just give a much better feel for the likely impact of a new building. They also make it possible to play SimCity with real urban areas.

Models that simulate sunlight throughout the day are just one kind of simulation that can potentially now be combined with a city-scale 3D landscape. "You could see exactly how a proposed building would affect the light available to your own house," Hudson-Smith says.

Other examples include simulations to warn of wind corridors or black spots in cellphone coverage.

"That's the sort of thing that large firms have worked on for years, but it generally required custom site surveys," says Hudson-Smith. City-scale maps will make it possible to explore "what if" scenarios across large areas at a low cost.

Skape maps have been used to flood urban areas with virtual water, a technique that will become much more powerful as 3D data for whole regions or countries becomes available.

Mapping work after the 9/11 attacks in New York provides another example. US firm Fuguro EarthData made Lidar scans of Ground Zero that were combined with architectural plans to recreate the perspectives of witnesses on the ground. Had 3D maps of the city been available in advance, the process would have been much simpler.

Competition between Google Earth and Microsoft's Virtual Earth to wow home users with 3D maps is partly responsible for the maturing of large-area 3D maps. But even as this technology goes pro, consumers may still have a role to play.

Google's newly launched Building Maker allows any web user to translate an aerial photo in Google Earth into a 3D building.

The results are less accurate than a Lidar-based map. But flying planes to get laser data is not cheap, says Hudson-Smith, so crowd-sourcing may be necessary outside commercial and urban areas.

Future maps may still need help from enthusiasts more interested in eye candy than urban planning.