The Substance Registry Services (SRS) is the authoritative resource for basic information about substances of interest to the U.S. EPA and its state and tribal partners. Substances, particularly chemicals, can have many valid synonyms. For example, toluene, methyl benzene, and phenyl methane, are commonly used names for the same chemical. EPA programs collect environmental data for this chemical using each of these names, plus others. This diversity leads to problems when a user is looking for programmatic data for toluene but is unaware that the data is stored under the synonym methyl benzene. For each substance, the SRS identifies the statutes, EPA programs, as well as organization external to EPA, that track or regulate that substance and the synonym used by that statute, EPA program or external organization. Besides standardized information for each chemical, such as the Chemical Abstracts Services name and the Chemical Abstracts Number and the EPA Registry Name (the EPA standard name), the SRS also includes additional information, such as molecular weight and molecular formula. Additionally, an SRS Internal Tracking Number uniquely identifies each substance, enabling cross-walking between synonyms. EPA is providing a large .ZIP file providing the SRS data in CSV format, and a separate small metadata file in XML containing the field names and definitions.

Travel Zones (TZs) are the spatial unit of geography defined by Transport Performance and Analytics (TPA), a business unit within Transport for NSW (TfNSW). The TZ spatial layer is applied to data sources used by TfNSW for transport modelling and analysis, including the Household Travel Survey and the Census 2016 Journey to Work data. The Australian Bureau of Statistics (ABS) Statistical Area boundaries form the foundation of the TZ. Generally, a TZ is larger than a Statistical Area Level 1 or Mesh Block, both ABS geography definitions. The ABS Statistical Areas are based on population counts whereas TZ boundaries are defined using population, employment, housing and transport infrastructure. TZs are designed to have standardised trip generation levels across all zones. This causes zones to be different sizes across the metropolitan area. As with many other spatial boundaries, TZs tend to be small in areas with high land-use densities and larger in areas of lower density. This dataset now includes a CSV file mapping the Transit Stop Number (TSN) to the Travel Zone (TZ16). It captures the stop name, suburb and coordinates. [Travel Zone Explorer](https://www.transport.nsw.gov.au/data-and-research/reference-information/travel-zone-explorer-visualisation) is an interactive map where you can search for Travel Zones (TZ) and find out the current and future population in occupied private dwellings by age and sex.