Built environment measures computed for Life Course Built Environment and Health participants
| Environment measure | Description | Core input data* and sources used | Processing required | Main output/s computed |
|---|---|---|---|---|
| Land use mix (Transport and Recreation) | Measures the diversity (or mix) and distribution of the area of destinations/land use classes of interest (eg, recreation vs transport land uses) against each other within a participant's service area. The creation of two land use mix measures reflect previous work by Christian and colleagues,47 which assessed land uses representative of transport and recreational walking. | Service areas, Cadastre, Land tenure information, Reserve Vesting Reports, (VGO points to identify residential features). | Land use classifications were developed from land tenure information (taxation/rating records) and reserve vesting reports. Nine categories of land use classifications were used to calculate two land use mix measures: (1) transport and (2) recreation. Land use was assigned to cadastral parcels on a mutually exclusive basis (with overlaps eliminated) based on a hierarchy of preference.47 | Area (square metres) for all nine land use types within a participant's service area. Land-use mix was calculated according to an entropy formula,47 which is a variation of that originally used by Frank et al48 |
| Street connectivity | Measures the inter-connectedness of the road (ie, street) network within a participant's service area. | Road network nodes representing three-way or more intersections, service areas. | Streets with ≥3 intersections were identified using road network data. | Count of three (or more) intersections divided by the area (square metres) of the participant's service area. |
| Road exposure | Proxy measure for the level of traffic volume on roads within a participant's service area. | Road network, Service areas, Functional Road Hierarchy (FRH) †information. | ‘Road function’ detailing exposure to number of vehicles/day was used as a proxy for traffic volume. | Total length (metres) of each road type within the service area. |
| Residential density | Measures the density of residential dwellings on residential land within a participant's service area. | Service areas, Cadastre, Land use (VGO points used to identify residential features). | Area of residential land within a service area was estimated by geographically selecting cadastral parcels that intersect VGO points classified as residential features. | Number of residential dwellings divided by the area of residential land (square metres) within the participant's service area. |
| Gross density | Measures the density of residential dwellings on participant's total service area. | Service areas, Land use (VGO points used to identify residential features). | Number of residential dwellings was obtained from VGO points classified as residential features. | Number of residential dwellings divided by the total area of the participant's service area (hectares). Not calculated for 1600m service area. |
| Lot density | Measures type of dwelling on the participant's residential lot. | Participant's geocoded home address, Cadastre, Land Use (VGO points). | ‘Lot type’ was computed using the spatial join tool in ArcGIS v10. Participant's homes that intersected cadastral parcels with VGO ‘dwelling’ information (eg, house, duplex, apartment) were identified. | Lot type classification (eg, house, duplex), Zoning information such as zonal code and classification, Residential dwelling (yes, no). ‘Lot density’ for each participant was determined by a count of ‘lot types’. |
| Greenness | Measures the presence of greenness in a neighbourhood. | Service areas, Normalised Difference Vegetation Index (NDVI) raster layer (25 m×25 m cells)‡. | Greenness was calculated using the Extract NDVI tool. Water features were removed before the NDVI values were calculated.11 | Minimum, maximum, mean, range, SD and sum for NDVI values within each participant's service area. |
| Slope (terrain) | Measures the on-ground terrain or topography. | Service areas, Digital Elevation Model (DEM) for slope (90 m×90 m cells)§. | Percentage slope was calculated from a 90m x 90m DEM using a spatial analyst tool, Slope. | Minimum, maximum, mean, range, SD, and sum for each service area from the slope raster that intersected the road network. |
| Walkability index 1 & 2 (not calculated in GIS) | Measures the ‘pedestrian-friendliness’ of a neighbourhood that is, how supportive a neighbourhood is of active living through encouraging walking for transport (for utilitarian reasons such as accessing destinations) or recreation (walking for fitness or enjoyment). | Index is comprised of standard z-scores for street connectivity, land-use mix and residential density. | Two walkability indices were created for each participant: (1) transport walkability index and (2) recreational walkability index, based on transport and recreation land use mix measures.47 | Walkability score (integers). Walkability quartiles. |
All environment measures were processed at 200, 400, 800 and 1600 m service areas around each consenting participant's home, unless otherwise specified.
Cadastre, Reserve Vesting Reports, VGO points and Road network data were provided by the Western Australian Land Information Authority.
VGO, Valuer General's Office.
*Core input data: refers to cadastre, road network, etc. The years of core input data which best reflects the year the participant completed the survey was used. For example, GIS core input data for years 2005, 2006, 2008 and 2009 were used for participants completing the survey in four groups respectively: (1) February 2003–June 2005; (2) July 2005–December 2006; (3) January 2007–June 2008 and (4) July 2008–December 2009.
†Functional Road Hierarchy (FRH): The hierarchy designated the function of all roads in Perth: (1) Access Roads (≤3000 vehicles/day); (2) Local Distributor (≤6000 vehicles/day); (3) District Distributor B (>6000 vehicles/day); (4) District Distributor A (>8000 vehicles/day); (5) Primary Distributor (>15 000 vehicles/day) and (6) Regional Distributor (>100 vehicles/day; connects metropolitan distributors 1–5 to regional areas).51
‡Normalised Difference Vegetation Index (NDVI) layer was derived from annually updated Landsat TM remote sensing imagery. NDVI values ranged from −1 to +1. Values of −1 generally represent water, while values of zero (−0.1 to 0.1) correspond to bare surfaces such as rock, sand, rooftops and roads. Higher values (0.2 to 0.4) represent grassland or bush land and values of +1 represent green vegetation.49
§Digital Elevation Model (DEM) layer for slope was provided by Geoscience Australia.50