The mechanism of self‐organization of agglomerations in a long narrow economy of a new economic geography model is elucidated by a theoretical comparative study with a racetrack economy. Computational bifurcation theory is used to systematically obtain the equilibria of these economies. A chain of spatially repeated core–periphery patterns à la Christaller and Lösch emerges when agglomeration forces are large. Peripheral zones are enlarged recurrently to engender an agglomeration shadow en route to an atomic mono‐center. A megalopolis with two core places connected by an industrial belt emerges when agglomeration forces are small.