What does this LiDAR map of London have to do with the rediscovery of a centuries-lost Roman Road in Lancashire, connecting Ribchester and Catterall?

Back in 43AD, after the Roman conquest of Britain, the Emperor Vespasian sent governor Quintus Petilius Cerialis to what's now Lancashire, Yorkshire and Cumbria to wrestle control of the north of England from a Celtic tribe called the Brigantes and put down a rebellion that had erupted after the breakdown of the marriage between Queen Cartimandua and her husband Venetius (she eloped with a 'common soldier'). These roads were an important part of connecting buildings and settlements to consolidate territory up north.

LiDAR mapping has helped to find four lost Roman roads so far, and there are hopes it will enable archaeologists to find many more - this 'light detection and ranging' laser mapping technology can be used to 'prove' the course a road took where before it was only suspected. LiDAR enables them to spot 'aggers' - Roman ramparts - running straight for a few kilometres, where a road must have been.


At present, about 75 per cent of England is mapped in this way, with limited knowledge of upland areas – the Environment Agency began LiDAR scanning 20 years ago as a means of tracking changing coastlines and performing flood modelling.

They have just announced plans to map the entire of England – which they say is the equivalent of about 32 million football pitches - by the end of 2020.

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To create LiDAR maps, aircraft with laser scanners measure the distance between the plane and objects it encounters. Instead of radio or sound waves, as in the case of Radar or Sonar, LiDAR - wait for it - uses light waves and 'velocity of time' to calculate the time it takes to hit an object and be sent back, building up a detailed picture of what is out there.

Firing about 1 million pulses per second, it processes them into a 3D visualisation called a 'point cloud'. (The above point cloud has been "coloured by elevation and intensity (strength of return)," says Susan Winter who works in Geomatics at the Environment Agency's National Monitoring Services.)

Using newer sensors that enable planes to fly higher and catch wider swathes of data, image capturing is more efficient, Winters says. In addition, "updated workstations and software allow for faster and more efficient throughput of data."


In 2015, the Environment Agency made the eleven terabytes of LiDAR surveys open Survey Open Data portal.

Beyond assessing flood risk, planning defences and understanding the natural landscape for varied purposes including those of archaeologists, the agency also hopes to fight "waste crime," which James Bevan, chief executive of the environment agency, has dubbed "the new narcotics".

Waste dumping reportedly costs £1 billion a year, with 1,000 sites discovered in 2015 - the process involves fraudsters dumping skip-loads of rubbish onto a piece of land and leaving it there to fester, while charging customers for the pleasure. LiDAR data enables authorities to discover sudden changes in the landscape quickly and crack down on the practice.