Data Quality

Positional Accuracy

Positional accuracy is an assessment of the closeness of the location of the spatial objects in relation to their true positions on the earth’s surface. Relative spatial accuracy of Roads reflects that of the jurisdictional source data. The accuracy is +/- 2 metres in urban areas and +/- 10 metres in rural and remote areas. Localised deviations from these accuracy metrics does occur and improvement programs are being undertaken to provide wide scale consistent data accuracy.

Coordinates Referencing the GDA2020 Datum

Spatial features referencing the GDA2020 datum are produced using a coordinate transformation from the GDA94 datum using the following parameters.

shift_x = 0.06155,
shift_y = -0.01087,
shift_z = -0.04019,
rotate_x = -0.0394924,
rotate_y = -0.0327221,
rotate_z = -0.0328979,
scale_adjust = -0.009994

Road Geometry Validity

Road geometry is validated to ensure Road lines are valid in the definition of their linear representation and free of self-intersection. Issues being detected and resolved include spikes, bow ties, duplicate vertices, null geometries, multipart geometries, self-closing lines and self-contacting lines.

Road Network Connectivity

Roads is a national roads product sourced predominantly from State and Territory scale datasets. The aggregation of isolated road networks into a single national network is focussed on providing the maximum consistency in road geometry and attribution across borders as well as ensuring the connectivity of Roads at State/Territory borders.

State/Territory Borders

All Roads at inland borders of States and Territories are manually reviewed for connectivity. Where disconnects in the road network were discovered and reference data exists to inform updates, then edits are applied to maintain connectivity.

Network Topology

Topology corrections are applied to the entire Road network. These corrections resolve issues introduced that impact the connectivity of the network and subsequently the networks applicability to any routing or journey planning activity. The specific issues detected and resolved through the topology rules are:

  • Undershoot: An undershoot occurs where a Roads segment is disconnected at one end from the Road network and that Road end is within 1 metre of another Road end. Where these occur, the Road is extended to connect to the nearest Road within one metre.

  • Overshoot: An overshoot occurs where a Road geometry crosses another Road geometry and ends within 1m of the other Roads feature. In these instances, the Roads are split at the intersection and are then assessed for small Roads < 1m that only connect to the network at one end, these small Roads are removed.

  • Duplicate Roads: Where two Roads have the same geometric representation and are attributed as the same Road then one of these Roads is removed.

  • Small Isolated Geometry: Where a Road has a length less than 100m and is not connected to the Road network at either end then this Road is not included within the Roads dataset.

  • Overlap: When a Road has part of its geometry overlapping another Road geometry this overlap is resolved. Where the Road continues along the linear representation of another Road this overlapping segment is removed from one Road. Where a Road is snapped to a vertex on an adjoining Road not at the end but then overlaps the adjoining Road to connect to the end then this snapping location is removed to resolve the overlap.