The catchment boundaries of 205 Tasmanian rivers were derived from 1:100,000 map sheets for an Ocean Rescue 2000 funded study , Regional Classification of Tasmanian Coastal Waters - Stage 2, EstuariesThe report for this study is titled " A Classification of Tasmanian Estuaries and Assessment of their Conservation Significance: an Analysis using Ecological and Physical Attributes, Population and Land Use" by G.J.Edgar, N.S.Barrett and D.J.Graddon, 1999.

Catchment boundaries were determined from contour lines and drainage courses shown on 1:100,000 topographic map sheets. The boundary or catchment divide is predicted by assuming that all surface flow occurs in the direction of the land slope, ie in a direction perpendicular to the contours. The boundary only intersects contour lines when it runs along a ridge. Catchment boundaries were traced from the most recent editions of LIB 1:100,000 topographic maps. Traced images were scanned, at a resolution of 300 dots per inch (dpi) on a flat bed scanner at the LIB, DELM. The images were imported into Arc/Info, then registered and rectified to AMG Zone 55 using the marked Tic points. Rectified grid based images were then vectorised using the Arc command Gridline.Vectorised coverages were cleaned to remove intersecting arcs and sliver polygons.Cleaned coverages were edge matched to neighbouring coverages then all individual map sheet coverages were appended to a single coverage of all catchment boundaries. The catchment coverage was then appended to the 1:25,000 coastline coverage. Estuarine catchment boundaries were joined to the coastline in order to close the polygon for each catchment. In 1998 the coverage size was reduced by using ArcInfo Generalize to 1 metre

Position Accuracy: The catchment boundaries derived are subject to error resulting from errors in the original map sheets, errors in defining catchment boundaries and errors in transcription of linework to digital coverage. The stated error in horizontal position on LIB 1:000,000 topographic map sheets is +/- 25 m. Errors in determining catchment boundaries are difficult to assess. In areas of steep topography (close contours), errors are likely to be of the same order as the error in the map-sheet. However in areas of shallow topography and indeterminate drainage representation, errors in catchment boundaries are likely to be high (up to 500 m). Small errors are introduced at all stages in transcribing catchment boundaries to digital coverages. A line width of 0.4 mm corresponds to 40 m at 1:100,000 scale. Scanning of this line at 300 dpi gives a line approximately 5 cells wide (cell size is ~ 8.5 by 8.5 m). For 42 map sheets, the average error recorded during rectification was 10.6 m, equivalent to a RMS error of 0.004 (Maximum error was 26.5 m, RMS 0.01).Vectorisation produces a line of zero thickness from the grid/cell image. Summing errors from determining catchment boundaries (+/- 50 m) and transcription (+/- 50 m) gives an approximate error of +/- 100 m. As noted above, this error may be considerably greater in areas of shallow topography. Attribute Accuracy: N/A Logical Consistency: All data is checked for undershoots, overshoots, duplicate elements, accurate symbology and free endpoints by both visual and automated means. Completeness: The Tasmanian mainland and major islands.