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Continuous and cyclic revision

Ordnance Survey has implemented a new approach to the way in which it revises its large-scale topographic data products.

The changes relate to the programme for revision of rural and moorland geography via cyclic revision (which is collected via aerial photography). The changes came partly as a result of ongoing investigation into ways in which to improve data collection and product revision as a whole within Ordnance Survey, but also due to the removal of funding for this activity, which was provided through the National Mapping Interest Service Agreement. This funding was withdrawn from Ordnance Survey in December 2006 by the Department for Communities and Local Government.

Since 1995, Ordnance Survey's approach to undertaking rural cyclic revision has been to complete 5 year cyclic sweeps where every 1:2500 rural tile is visited once in each cycle. Also under this programme all 1:10,000 mountain and moorland tiles were visited once in the 10 years spanning the two cycles.

Since 2007, a new approach has been followed for revision of rural and moorland geography. The process of cyclic revision via aerial photography is still adopted, but the way in which the resulting 'sweeps' are scheduled is driven by change intelligence (information about where change will occur in the landscape). The new programme uses change intelligence and other socio-economic indicators (e.g. population and road density) to sub-divide UK according to the frequency at which they will be revised using aerial photography. The new programme provides each geographic division with a revision timeframe ranging from 2 to 10 years. The divisions are reviewed on a regular basis according to the change information that is received. This approach means that all areas within UK are revised at least once per 10 years, with some being revised as much as every two years. The programme also ensures that Great Britain as a whole is swept for cyclic revision in its entirety every 10 years.

Continuous revision involves the recording of significant new features within our central database. It is a fundamental activity that ensures high-quality current mapping is available for all parts of the country. The key method that is employed in the collection of this data is ground survey. We use several sources of intelligence to identify change on the ground including new construction, demolition and major changes to existing real world features. The intelligence on known change is recorded as a specific work package with a predicted completion date. The work packages are reviewed regularly with the objective that all known change will be captured in the database within 6 months of completion. The position of the features and attributes are then established and recorded in the National Geographic Database from which Ordnance Survey information is derived.

Cyclic revision has traditionally been managed as a national sweep programme aimed at ensuring that all 222,000 kms2 of rural, mountain and moorland areas are kept up to an agreed currency level - 5 years in rural areas and 10 years in mountain and moorland areas. The sweep programmes survey changes to the rural geography which are not captured by the continuous revision process, such as boundary changes and non-residential small buildings.

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