Is a geographic concentration of interconnected businesses, suppliers, and associated institutions in a particular field. Clusters are considered to increase the productivity with which companies can compete, nationally and globally. In urban study, the term agglomeration is used. This term industry cluster, also known as a business cluster, competitive cluster, or Porterian cluster, was introduced and the term cluster popularized by Michael Porter in The Competitive Advantage of Nations (1990). The importance of economic geography, or more correctly geographical economics, was also brought to attention by Paul Krugman in Geography and Trade (1991). Cluster development has since become a focus for many government programs. The underlying concept, which economists have referred to as agglomeration economies, dates back to 1890, and the work of Alfred Marshall.