We interpret fluctuations in GNP and unemployment as due to two types of disturbances: disturbances that have a permanent effect on output and disturbances that do not. We interpret the first as supply disturbances, the second as demand disturbances. Demand disturbances have a hump-shaped mirror-image effect on output and unemployment. The effect of supply disturbances on output increases steadily over time, peaking after two years and reaching a plateau after five years.

This Paper develops a model of economic growth and activity locating endogenously on a 3-dimensional featureless global geography. The same economic forces influence simultaneously growth, convergence, and spatial agglomeration and clustering. Economic activity is not concentrated on discrete isolated points but instead a dynamically-fluctuating, smooth spatial distribution. Spatial inequality is a Cass-Koopmans saddlepath, and the global distribution of economic activity converges towards egalitarian growth. Equality is stable but spatial inequality is needed to attain it.