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Taking Stock of Changing Broadland. I. Air Photointerpretation and Digital Cartography

1986; Wiley; Volume: 13; Issue: 4 Linguagem: Inglês

10.2307/2845015

1365-2699

R. M. Fuller, Nicholas Brown, M. D. Mountford,

Rangeland and Wildlife Management

Broadland was mapped from 1:10,000 scale, black-and- white, aerial photographs, using a transfer-instrument to provide optical correction of scale and tilt distortions. The maps showed fourteen seminatural habitats, three cultivated land uses, six types of developed land, and waterways, to a 10-20m resolution, plus linear features such as ditches, tracks and waterside piling. The map outlines were manually digitized to convert them into feature-coded lines of x- and y- coordinates, stored in a computer compatible form. The digital data were used to drive a light projection plotter to make high quality output maps. Data also allowed the areas of land and water parcels, and the lengths of linear features and habitat boundaries to be calculated. The accuracy of maps and data was checked against a sample of quadrats, photographed from the air, at high resolution. Area data were checked against available, equivalent, Ordnance Survey values. Line length data were checked by comparison with a manually measured sample. Results show the overall accuracy to be 88?3%, that the simplification inherent in the maps accounted for much of the apparent error, and that line lengths and area data contained only minor errors, which became negligible in the data summaries. The results overall show that only 30% of Broadland is seminatural, that, ecologically, the most important habitats occupy only 13% of the flood plains, and that much of this remaining area is likely to be lost, without preventive management. The data have subsequently been used to construct a word processor- stored data base, for use in management and monitoring by the Broads Authority. Initial experiments, which integrated the data, converted into raster-form (i.e. as grid cells), with airborne and satellite, remotely- sensed, imagery, show that such imagery may be useful in updating the Broadland dataset, in future.