Table 1 Metrics for quantifying spatial accessibility

Distance-based metrics:

Distance to nearest one destination or a group of nearby destinations

 - Euclidian distance (also known as flight or straight-line)

 - driving distance (also known as street network distance, which accounts for street network lengths and connectivity)

 - driving time (which further accounts for speed limits for each segment of the street network)

Container-based metrics:

Number of destinations within a pre-specified area or spanning distance or some spatial density measures including but not limited to:

 - per 1000 population

 - per area unit (e.g. square miles)

 - per road miles

Spatial interaction (gravity) model-based metrics:

 - Choose distance metrics

 - Define distance decay function and distance decay parameter

 - Specify the destination choice set within an area or spanning distance

 - Construct spatial accessibility index

Population-weighted accessibility metrics:

Aggregate spatial accessibility index weighted by population

 - Euclidian distance

 - driving distance

 - driving time

Population-weighted distance metrics:

Use spatial accessibility index to define differential probability access to destinations in the choice set and further weighted by population

 - Euclidian distance

 - driving distance

 - driving time