only good news was that nobody else picked up that $100 bill lying on the sidewalk in the interim." This would become Krugman's most-cited academic paper: by early 2009, it had 857 citations, more than double his second-ranked paper. Krugman called the paper "the love of my life in academic work". The "home market effect" that Krugman discovered in NTT also features in NEG, which interprets agglomeration "as the outcome of the interaction of increasing returns, trade costs and factor price differences". If trade is largely shaped by economies of scale, as Krugman's trade theory argues, then those economic regions with most production will be more profitable and will therefore attract even more production. That is, NTT implies that instead of spreading out evenly around the world, production will tend to concentrate in a few countries, regions, or cities, which will become densely populated but will also have higher levels of income. Agglomeration and economies of scale Manufacturing is characterized by increasing returns to scale and less restrictive and expansive land qualifications as compared to agricultural uses. So, geographically where can manufacturing be predicted to develop? Krugman states that manufacturing's geographical range is inherently limited by economies of scale, but also that manufacturing will establish and accrue itself in an area of high demand. Production that occurs adjacent to demand will result in lower transportation costs, but demand, as a result, will be greater due to concentrated nearby production. These forces act upon one another simultaneously, producing manufacturing and population agglomeration. Population will increase in these areas due to the more highly developed infrastructure and nearby production, therefore lowering the expense of goods, while economies of scale provide varied choices of goods and services. These forces will feed into each other until the greater portion of the urban population and manufacturing hubs are concentrated into a relatively insular geographic area. International finance Krugman has also been influential in the field of international finance. As a graduate student, Krugman visited the Federal Reserve Board where Stephen Salant and Dale Henderson were completing their discussion paper on speculative attacks in the gold market. Krugman adapted their model for the foreign exchange market, resulting in a 1979 paper on currency crises in the Journal of Money, Credit, and Banking, which showed that misaligned fixed exchange rate regimes are unlikely to end smoothly but instead end in a sudden speculative attack. Krugman's paper is