Keeping Ordnance Survey on the map

Thursday 19 April 2007, 18.30

Dave Lipsey, Information Systems Infrastructure Manager, Ordnance Survey


Thanks to an excellent talk by Dave, those who attended now have some understanding of how data is gathered and processed, how much data is involved, how things have changed during the history of Ordnance Survey and where it might go in the future. Dave’s talk was very interesting and instructive and was supported by a Pathe News film from 1961 and a large number of maps and photographs from various periods.


OS was formed in 1791, the first map was produced in 1801 and by 1893 maps cost 1s 6d. In 1935 Major General McLeod re-triangulated the grid from the white trig points on hills. In 1967 they started to digitise the maps to aid editing, which took 22 years.

In 2001 Digital OS Master Map was born. Everything has a topographical identifier e.g. your house, your garden and the lamppost in the street have separate topographical identifiers. There are about 450 million in an Oracle database (compared to 23 - 24 million unique addresses).

Data collection and aerial photography

The aim is to fly over the whole country (at about 100 feet) every three years with a huge digital camera (104Mpixels). Each frame is about 700Mb and there are about 2,000 frames per flying session. The flight path overlaps by about two-thirds to get a stereoscopic image; you can click on a building to get a height measurement.

Edges and colour are matched to give a “true” digital image then the mapping data is updated to correspond with that image. To enable the operators to see a stereoscopic image they wear glasses with the lenses polarised at 90 degrees to each other.

By manually comparing images of e.g. Wembley Stadium taken one year apart one can assess the amount of building work that has been done. This is known as change intelligence.

Data storage

The 200,000 limestone maps in racks (accessed by two men with pulleys) have been replaced by a SAN with about 650TB. People are more dependent on the data now so they have resilient systems. OS is using ultra dense optical media, each taking 30GB, to archive data, some of which needs to be kept for 100 years or more. They also use data de-duplication to achieve high compression ratios.

The future

Ideas include:

  • Super accurate (to 1 to 2cm) GPS - could be used to tell you to move one lane left (rather than “keep left”) or on building sites to map the location of foundations, etc.
  • Automated comparison of an old image with the current image to assess new build and demolition (automated change intelligence)
  • Real-time updating of geospatial data from surveyors in the field
  • Autosurveying technology in buildings e.g. have a gadget that “knows” when an extension is built


The evening ended with a lively question and answer session, including a discussion about writing software in-house or buying software when an organisation has unusual requirements.