Large area vegetation mapping in the Gisborne district, New Zealand, from Landsat TM

Debate over a forestry incentive scheme in the Gisborne district, New Zealand, highlighted the need for up to date information on the vegetation cover. Maps of vegetation at a scale of 1:100 000 were produced by automatically classifying Landsat Thematic Mapper (TM) imagery. The classified imagery was compared with existing vegetation information (20-years-old) from a GIS database to identify gross errors. Through field checking the discrepancies were identified as either real changes or errors in classification. Correction of errors increased the overall classification accuracy from 84 to 90 per cent. The digital vegetation map was intersected with land use suitability data to provide a two-way table that provided land managers with quantitative information suitable for making regional planning decisions. Although the 90 per cent accuracy is high enough to permit the calculation of vegetation areas and to achieve an adequate representation of regional vegetation patterns, it is not high enough to permit the digital vegetation map to be used as a vegetation database where point queries are important.