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Table 2 Definitions of different impedance measures

From: Methods to measure potential spatial access to delivery care in low- and middle-income countries: a case study in rural Ghana

Impedance measure Units Definition Data type GIS tool
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
  1. *GlobCover 2009 [24], GEM European Commission project [25].