Macquarie Island Vegetation and Drainage Structure Data Set

Full description

The data for this map were collected as part of two ASAC projects - 488 and 956, of which Patricia Selkirk was the chief investigator. Macquarie Island (54 degrees S 159 degrees E) is a subantarctic island (c. 35km by 3 to 5km) approximately equidistant between Tasmania, New Zealand and Antarctica in the Southern Ocean. The vegetation is herbaceous, lacking shrubs and trees. Vegetation and drainage are mapped at a scale of 1:25 000 from field observations, satellite imagery and limited oblique and aerial photography. The categories adopted for mapping vegetation are based on attributes of foliage height and percentage foliage cover of the ground surface (vegetation structure), not on species distribution (floristics). The distribution of vegetation categories is strongly correlated with aspect, topography and rock type. Mires, streams and lakes form an intricate drainage pattern that is strongly influenced by the geology of this tectonically active emergent crest of the submarine Macquarie Ridge at the boundary of the Pacific and Australian plates. The drainage pattern of the whole island is represented in a map with substantially greater accuracy than in any previous map.

Lineage

Progress Code: completed

Statement: Completeness of coverage: 100%. Completeness of classification: All categories generalised. All categories could be further subdivided. Some amalgamation of areas smaller than 30-50m diameter. Completeness of verification: 75%. Completeness of coverage. The data coverage is complete for the entire dataset. Attribute data are available for the entire dataset. Completeness of classification. The adopted classification method covers all features. Completeness of verification. The Polygon boundaries in some cases were generalised at the discretion of the Botanists from Macquarie University and data considered too small was omitted. Verification of features was carried out by Macquarie University using their extensive field notes and many years of local knowledge and experience. In preparing this map, we have used as a basis the SPOT 3 merged pan/multispectral image of 22 December 1994 and the coastline prepared from this image by AUSLIG (now Geoscience Australia). We have consulted the black and white aerial photography of 6 and 7 February 1976, runs CAS 5465, CAS 8467 to 8473 and CAS 8480 to 8483. We have drawn extensively on our fieldwork and on our own and colleagues' field notes and photographs. The original digitised source data were acquired in DXF format and then corrected and enhanced by Macquarie University personnel. Definitions and descriptions were added of the Terrestrial and Marine categories as provided by Macquarie University personnel. Software used for this process was 'microstation' and 'polygen'. The final product was completed in 'Arc View' and presented at a scale of 1:25,000. All data checked for polygon closure, etc, in Microstation to create the DXF file. All lines were visually checked at 1:25 000 scale to verify that no lines crossed. The GIS package (ArcInfo) was used to do topological consistency check to detect flaws in the data structure and to flag them as errors. This check insures that all classified polygons are closed, nodes are formed at the intersection of lines and that there is only one label within each polygon, etc Structural vegetation boundaries and position of drainage lines drawn from satellite imagery, some aerial photography and field knowledge. Horizontal positional accuracy (intuitive) is 50m. The data have been formatted according to the SCAR Feature Catalogue which includes data quality information (refer to link below). Usually mapped to a Universal Transverse Mercator projection, Zone 57. In 2000 the line data representing escarpments was edited by the Australian Antarctic Data Centre (AADC). A section near Bauer Bay was deleted as it was concluded this section of escarpment did not exist. The AADC has used the revised escarpment data in the 1:50 000 maps of Macquarie Island it has produced since then.