This paper attempts to present a basic model and corresponding weak and strong stability conditions of per-capita income in a multi-regional economy. Our basic postulate is that the elasticities of interregional movements of labor and capital discounted by average distance are constant. Based upon this theoretical postulate we present the stock and flow representations of basic models, and define a general M-economy and a prototype P-economy. Stability conditions of per-capita income differences and tendencies of regional shares of absolute income are discussed within these models. A remarkable conclusion is that the share of the absolute income shows an unbalanced growth while the stability condition is satisfied and per-capita income is equalized overtime. Finally the model is extended by treating investment as endogenous.