How OS expert mapmakers see the world differently

Researchers at Aston University have found differences between experienced Ordnance Survey (OS) mapmakers and novices in the way that they interpret aerial images for mapmaking, which could lead to improved training processes for new recruits. 

OS is well known for its travel and walking maps, but is also responsible for maintaining Great Britain’s national geographic database. Every time a building is demolished or developed, or a new road and path built, the map must be updated.   Aerial photographs are taken of the area that has changed, either from a plane or using drones, and expert mapmakers, known as remote sensing surveyors, will examine the images to identify change and accurately redraw the map of the area.   Image pairs are presented stereoscopically, one to each eye, allowing the remote sensing surveyors to see in 3D and correctly assess the topography, such as ditches, hills and hedges.  

Led by Professor Andrew Schofield, a team from Aston University’s College of Health and Life Sciences, together with Dr Isabel Sargent, previously at OS, carried out a study to understand how remote sensing surveyors interpret the shadows and highlights in images.  The researchers asked six trained remote sensing surveyors and six novices to assess 10,000 stereoscopic aerial images of hedges and ditches, which had been heavily masked with image distortions.  

The stereoscopic images the aerial surveyors use for mapmaking are usually taken on sunny days. The human brain is naturally wired to interpret light as coming from above. However, the light does not come from above in the OS aerial images, it depends on the position of the sun. In the UK, north of the equator, light comes slightly from the south, thus appearing to come from below in images viewed by the surveyors.  The researchers wanted to see how manipulating the direction of the light would affect the surveyors.