Later on, Krugman became interested in economic geography, in the related question of why there were regional specialties—why, in the United States, for instance, were cars produced in Detroit, carpets in Dalton, Georgia, jewelry in Providence, and chips in Silicon Valley? Again, the answer turned out to be history and accident. Once an industry started up in one place, for whatever reason (the carpet industry in Dalton appears to have its origin in a local teen-ager who in 1895 made a tufted bedspread as a wedding present), local workers became trained in its methods, skilled workers from elsewhere moved there, and related businesses sprang up close by. Then, as more skilled labor became available, the industry could grow and benefit from economies of scale. Soon, as long as it didn’t cost too much to transport the industry’s products, the advantages of the place would be such that it would be impractical for someone to open up a similar business anywhere else. Many economists found the idea that economic geography could be so arbitrary “deeply disturbing and troubling,” Krugman wrote, but he found it exciting.
Again, as in his trade theory, it was not so much his idea that was significant as the translation of the idea into mathematical language. “I explained this basic idea”—of economic geography—“to a non-economist friend,” Krugman wrote, “who replied in some dismay, ‘Isn’t that pretty obvious?’ And of course it is.” Yet, because it had not been well modelled, the idea had been disregarded by economists for years. Krugman began to realize that in the previous few decades economic knowledge that had not been translated into models had been effectively lost, because economists didn’t know what to do with it. His friend Craig Murphy, a political scientist at Wellesley, had a collection of antique maps of Africa, and he told Krugman that a similar thing had happened in cartography. Sixteenth-century maps of Africa were misleading in all kinds of ways, but they contained quite a bit of information about the continent’s interior—the River Niger, Timbuktu. Two centuries later, mapmaking had become much more accurate, but the interior of Africa had become a blank. As standards for what counted as a mappable fact rose, knowledge that didn’t meet those standards—secondhand travellers’ reports, guesses hazarded without compasses or sextants—was discarded and lost. Eventually, the higher standards paid off—by the nineteenth century the maps were filled in again—but for a while the sharpening of technique caused loss as well as gain.