Channel migration is a fundamental, yet incompletely understood, aspect of the dynamics of meandering rivers. Current theoretical models aimed at predicting planform dynamics relate rates of meander migration to local and upstream planform curvature where weighting of the influence of curvature on migration rate decays exponentially over distance. This theoretical relation, however, has not been rigorously evaluated empirically. Furthermore, predictive models based on this relation are incapable of reproducing complex forms of bend development, such as compound loops. This paper presents the development of a methodology based on parametric cubic splines for investigating empirically the relationship between spatially extended curvature and local bend migration for a study reach along a highly sinuous section of the Embarras River in Illinois, USA, which contains compound loops. Results indicate that the spatial structure of migration rate-curvature relation may be more complex than currently is assumed. The study provides a first step toward unraveling the spatial structure of planform evolution of meandering rivers.