Primary Activities
	Secondary Activities
	Tertiary and Quaternary Activities
	Economic Revolutions
	U.S. Employment by Economic Sector
	Number of U.S. Farms
	Average Size of U.S. Farms
	Use of Land in the U.S.
	Pittsburgh Region Jobs
	Additional Jobs in the U.S.
	Job Gains and Losses in the Pittsburgh Region
	Per Capita G.N.P.
	Rostow's Stages of Development
	Shifting Cultivation
	Share of Grain Consumed by Livestock
	Determinants of Agricultural Regions
	J. H. von Thunen's Model
	Spread of the Industrial Revolution
	Spatial Margin of Pofitability
	Economic Location Factors
	Transportation Costs
	Freight Carried by Railway and Truck