ABSTRACT
Although widely accepted, API has several disadvantages, namely: (i) Imagery, if available at all, may only be available for specific dates. If no imagery exists for a chosen area there may be high costs involved in planning and executing a flight; (ii) The interpretation process is time consuming and laborious, especially for complex areas such as the sub-urban landscape. The time taken depends on the level of classification which in this case is detailed; (iii) The interpretation is likely to contain uncertainty (both thematic and geometric) as a result of user subjectivity, digitising errors and properties of the photograph itself (e.g. scale, geometric registration). The use of orthophotos can help alleviate the latter problem. Interpretations of the same area by different observers may be quite different and (iv) Expert knowledge is required
to correctly label the polygons (this may be provided by additional field survey or ancillary data).
