Contents & Foreword, Characterizing And ... - IRRI books

ming the distance of all line segments constituting the route between the origin andtarget locations. This requires an infrastructure map that is properly formatted as atopologically consistent network connecting the points of origin (farms/villages) withthe target or destination points (markets, schools, etc.). In remote areas, not all locationsare served by roads, or sometimes details of tracks are not provided in smallscaleroad maps. Auxiliary information such as topography, hydrography, and landcover can be used to model the “least-cost” pathway access from a remote location toexisting mapped roads. The least-cost pathways identified in a GIS can also be usedto supplement sparse road networks and provide travel distance data for better estimationof accessibility in areas with poorly developed transportation infrastructures.Where the quality of transport infrastructure varies across the network and enablesdifferent ease of transit across it (e.g., dirt roads must be traveled at slowerspeeds than well-maintained paved roads, so that the dirt roads have a higher “impedance”),accessibility measures based solely on travel distances are poor indicators ofaccessibility. One way to incorporate differences in the ease of transport along differentsegments of the network is to “tag” the travel speed or travel times to these segments,and compute the total time taken to traverse along the network from the originto the target location. The term “travel cost” is used to refer to the distance, time, orfinancial cost to get from an origin to a target location.The ease of transporting goods from the farm gate to the market should reflectthe overall ease of transport between the farm and all the available local markets,rather than the distance or time to transport goods to the market that happens to beused by the farm at one time. Accessibility indicators calculated using several referencemarkets are preferable because they reflect the exogenous availability of marketsin a particular area rather than the endogenous outcome of a farm’s choice to buyor sell goods/factors at a particular market. GIS-based analysis allows for easy computationof quantitative indicators that reflect overall accessibility from the farm (orvillage) to multiple markets. The average travel cost index is an example of this typeof indicator. The average travel cost index D i for an origin location i is the mean travelcost between the origin location (e.g., village) and a number (J) of target locations(e.g., markets):D i = Σ d ij /JJj = 1where D i = average distance (in km) between farm i and the J target market(s) and d ij= length/distance of the line segment k (in km) between the village and market j.Closely related to the effect transport costs play in determining the level offarm production and the extent of subsistence orientation of farms, transport costsalso determine what crops farms cultivate and the intensity of land use on the farm.For example, farms in remote areas may be prevented from economically cultivatingfresh produce by the cost and speed required to transport output to the market. Due tothe ease of storing rice, the commodity is often particularly favored in remote areas.Agricultural marketing channels in remote areas often focus on rice. As a result, evenIntegration of biophysical and socioeconomic constraints . . . 449