The referral analysis allows one to compute the travelling times and/or the distances along the least-cost paths (i.e. path between two locations that minimizes the total travel duration for those travelling along it, see Ray and Ebener, 2008) between two groups of health centers. Such path is different from a straight line as it does take into account the landscape constraints together with the modes and speeds of travel of the population.
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(5) The "Permute group" option allows one to improve computation time when more facilities are selected in the starting group than in the destination one. But if this option is selected, 'Limit the spatial analysis to the closest pair time-wise' is not possible. We will not use this option for the exercise.
(6) The option "Output the layer of the paths among selected facilities", if checked, will output a polyline shapefile with all least-cost paths among all the start-destination pairs of points.
(7) The "Enable parallelization" option, if checked, allows the referral analysis to be parallelized on all available CPUCPUs/Core cores that your AccessMod isntance has access to. If you are using Virtual box, the numbers of available cores can be changed in the settings of VirtualBox. Using this option can drastically decrease the overall computation time for this analysis.
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