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Spatial accessibility is described as the capacity to reach the surrounding areas from a specified location (Luo and Wang, 2003; Ahlström et. al., 2011). Sometimes identified as transferability, spatial accessibility is a key component in establishing the physical interaction between places (Theriault et al. 2005; Rodrigue et al., 2013). The other components include complementarity (supply and demand between the interacting locations) and intervening opportunity (presence or absence of better alternatives) (Rodrigue et al., 2013). For spatial access to be established, the place of origin and destination must be physically linked through some sort of transport infrastructure such as road or rail (Olsson, J. 2009; Ahlström et. al., 2011; Rodrigue et al., 2013). Where transport infrastructure is limited or unreliable, spatial accessibility is negatively affected, and ultimately, constrains interaction severely within the region and beyond (Roehner, 1996; Guimarfies and Uhl, 1997; Porter, 2002b; Nutley, 2003).
In the developing world, the lack of adequate and reliable transport infrastructure is widespread, particularly, in rural areas. This phenomenon is considered as one of the main obstacles to economic development in various regions around the world (Guimarfies and Uhl, 1997; Porter, 2002b; Nutley, 2003; Olsson, 2009). Sub-Saharan Africa (SSA) for example, is considered as the worst accessible region in the world in terms of road density (Buys et al., 2006; Gwilliam, 2011) (figure 1). SSA has an average road network density of 3.4 km per 1,000 people, compared with the world average of 7.1 km (Gwilliam, 2011). Motorable roads form a small portion (about 34%) of rural road network but almost half are in deplorable conditions (African Development Bank (ADB), 2010). The remainder include tracks or paths that link local communities to farms and market centers (Riverson et al., 1991).
Figure 1. Global spatial density of road networks
The lack of adequate and reliable roads in SSA has been blamed for limited access to necessary amenities like schools, clinics, and market centers (Riverson et al., 1991; Porter, 2002(b)). It also led to persistent low agricultural productivity, poor food distribution (World Food Program, 2009; Gwilliam, 2011) and minimal trading opportunities (Hoyle and Knowles, 1998; Lamport, 2009) in the sub region (Naude et al., 1999). With agriculture being the principal economic activity in SSA (World Bank, 2008; Abatena, 2009; Gwilliam, 2011), it is crucial to study and address the issue of poor spatial accessibility.