The size of migration corridors is typically compared based on the size or rate of the flow. Migration flow counts fail to control for heterogeneity in the population size of regions. Migration rates (or intensities) adjust for population size of either the sending or the receiving region, but not both. To this end, this paper proposes two alternative measures of bilateral migration that express the size of origin-destination corridors in relation to the total migration flows during a period or the total population. The proposed Standardized Migration Affinity (SMA) index and Standardized Migration Velocity (SMV) index enable us to describe migration systems of different geographical scales and identify prominent migration corridors that are disguised when studying bilateral migrant flow counts or rates. Using examples of internal migration in China, we illustrate the application of the proposed measures at various geographic levels
