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Master of all it surveys

To improve the accuracy of the Ordnance Survey, the CODES scheme now pays architects for detailed information We think of the Ordnance Survey (OS) as the rock of British mapping.

And so it is - up to a point. Now it is giving architects the opportunity to contribute to the greater precision of this national institution by filing site plans of their recent projects with a two-year-old initiative, Ordnance Survey CODES (the Collection Of Data from External Sources) at www. ordnancesurvey. co. uk/codes.

We live in public-private initiative times so there is a modest fee paid in exchange for providing information - £8 per house, with a minimum of five, and £75 per hectare for non-housing sites. It is not a lot but on a big scheme it can mount up.

The OS is especially important for HM Land Registry, which guarantees the title to property in England and Wales. It refers matters of accuracy to the OS people but it also points out (at www. landreg. gov. uk/publications/ el/el024. pdf ) that because of the scale at which even big OS maps are drawn, a single boundary line on a map might well be as wide as a hedge or a ditch on the ground. Not least on these grounds, it urges potential boundary disputants to try to resolve arguments without recourse to the courts. So although the basis for site boundaries sounds as if it is cut and dried by high authority, the reality is a little less precise.

Gian Kundei at Tooley & Foster says: 'The OS is OK as far as feasibility studies are concerned. But before we start serious work on a project we always commission a 3D digital survey.' It is a position shared by all the architects I have spoken to who are involved in the scheme. One says: 'All our clients have site surveys done by land surveyors. OS can't possibly check every boundary.'

So when developers have a site survey done they could be contributing to the greater accuracy of the OS.

And the system will become more efficient the more digital information becomes available. It is this kind of really precise survey material, based on aerial photography, GPS and a variety of super-accurate surveying methods that the OS is now harvesting under the CODES initiative.

How does it work?

Steve Reeves, OS CODES manager, explains: 'We sign a licence agreement for OS to use the copyright owner's material in return for the fee.We have the design drawings emailed in to us in AutoCAD format and we assess it, so that it can be incorporated in our database.'

It is here that, as a kind of perk, OS can pick up any discrepancies and agree corrections for early Land Registry approval. There is no need to remove hatching or shading or other detail from the electronic drawings because the OS people reduce them to the OS standard.

'We're interested in anything that will affect OS mapping - internal alterations aren't relevant but extensions to buildings are, ' Wright says.

He reports that in the past two years CODES has signed up 250 organisations. 'Our target last year was 50 per cent of all major developments, which we define as greater than 1ha and greater than five houses.We have achieved that over the time. At the moment we are receiving, on average, up to 10 sites a day from a whole mix of suppliers. But we are looking for a greater residential element, and for more architects to come on board.'

Doing it Paul Wainwright at the Leeds office of Chetwood Associates, which is signing up for another year on the CODES scheme, explains how his practice got involved. 'We had a cold call from OS, who floated the idea that it spends a lot of time and assets in surveying sites but that much of the information is all there now, ' he says.

'Here was an opportunity to cut out the middleman, especially when the data is on CAD.We lay out a lot in purchasing this data in the first place.

So now OS pays us more or less what we would pay out.We are quite a large architectural practice. Our jobs tend to be multimillion projects. Given the kind of work we do, the fee can be a quite sizeable amount. We're a commercial business, and the benefit [of signing up with CODES] is that we can offset some of our initial outlay.'

'The thing that surprised me at the beginning was that OS was asking for drawings that had achieved planning consent. Things change quite markedly in the progress of a project and we have to go back to the planners from time to time. So what we furnish the OS with can change during the progress of a job.'

Wright explains: 'We ask for the data only after detail planning has been achieved, and ask that the suppliers update. They can supply us with the as-built data and we pay half as much again. But our surveyors will go out and verify what has been built.'

This serves as a reminder that CODES is not a substitute for the main task of the OS, and each evening its surveyors across the country feed data into its big database, as the face of the country slowly changes.

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