TPA has a range of location information products which include digitised boundaries. Travel Zones (TZs) are the geographic units of TPA’s data collection, transport modelling and analysis. They are designed to align as much as possible with current Australian Bureau of Statistics (ABS) geographic classification for that year, to allow for comparison of different data sources at standard geographies. In order to provide for a similar level of trip generation across zones, TZs are designed to be small in areas with high land use densities and larger in areas of lower density. The key land uses of interest in defining TZs are employment, housing and transport infrastructure. As urban areas change over time, TPA creates a new zoning system in line with each 5-yearly population Census. Digitised boundaries for these zoning systems and equivalences between them, are available to users to undertake spatial analysis. 1991 – 2006 – Australian Standard Geographical Classification (ASGC), with Statistical Local Areas (SLA), Census Collection District (CCD) and Mesh Blocks (MB). Prior to 2006, TZs aligned to Statistical Local Areas (SLA). GMA may change slightly at the boundary to align with ABS geographic classifications. This will not usually impact on the comparison of data over time.