The document discusses the economic base theory, which states that a region's economic growth is determined by the increase in exports from that region. It defines base industries as those that produce goods or services for markets outside the region, bringing in outside money, while non-base industries serve the local region. The economic base multiplier is used to calculate total employment changes resulting from changes in base employment. Methods for determining base industries include direct surveys of firms, indirect assumptions, and location quotients comparing a sector's share of regional employment to its national share. The economic bases of cities typically include services and trade, while rural regions often rely on agriculture, mining and manufacturing as their bases.