Table 2 Definitions of different impedance measures

Euclidean distance

Km

Straight-line distance from population to closest health facility

Vector

Near

Network distance

Km

Distance along road network from population to closest health facility, plus Euclidean distance to the road network from the population, and from the road network to the health facility

Vector

Network analyst closest facility

+ Near

Mechanized network time

Hour

Distance along road network from population to closest health facility multiplied by driving speed on roads, plus Euclidean distance multiplied by off-road walking speed (2 km/h) to the road network from the population, and from the road network to the health facility

Vector

Network analyst closest facility

+ Near

Non-mechanized network time

Hour

Distance along road network from population to closest health facility multiplied by walking speed on roads (4 km/h), plus Euclidean distance multiplied by off-road walking speed (2 km/h) to the road network from the population, and from the road network to the health facility

Vector

Network analyst closest facility

+ Near

Mechanized raster time

Hour

Travel time from population to closest health facility, assuming mechanized travel on roads and non-mechanized travel off road according to land cover speeds*, 200 m x 200 m grid

Raster

Least-cost path

Non-mechanized raster time

Hour

Travel time from population to closest health facility, assuming non-mechanized travel on roads (4 km/h) and off roads according to land cover speeds*, 200 m x 200 m grid

Raster

Least-cost path