Evaluating Spatial Interaction Models for Regional Mobility in Sub-Saharan Africa
Fig 4
The results of fitting each spatial interaction model.
A) The predicted results from both gravity and radiation models. The gravity model (shown in blue) predicts larger amounts of the total volume of travel over the course of the data set (ratio of predicted values to data–mean: 12, 95% quantile interval: 0.34–43) than the data whereas the radiation model (shown in red) underpredicts the volume of travel (ratio of predicted values to data–mean: 0.5, 95% quantile interval: 0.0066–1.7). B) The ratio of predicted versus actual data from both models versus distance. For both models, the predictions over short distances were worse than over longer distances. C) We re-fit gravity models using Euclidean distance (red), travel times (blue) and road distance (green) between district centroids (circle) and population-weighted district (square) centroids. The reduction in deviance of these models is shown. In general, Euclidean distance based gravity models outperformed all other distance measures, except for travel between rural areas. For this type of travel, road distance outperformed Euclidean distance (Euclidean distance–reduction in deviance: 63%, road distance–reduction in deviance: 72%, see Supporting Information).