The most complex node is the "global city", with links binding it to other cities having a direct and tangible effect on global socio-economic affairs. The term "global city", rather than "megacity", was popularized by sociologist Saskia Sassen in her 1991 work, The Global City: New York, London, Tokyo. "World city", meaning a city heavily involved in global trade, appeared in the May 1886 description of Liverpool, by The Illustrated London News. Patrick Geddes later used the term "world city" in 1915. More recently, the term has focused on a city's financial power and high technology infrastructure, with other factors becoming less relevant.
Global city status is considered beneficial and desirable. Competing groups have developed multiple alternative methods to classify and rank world cities and to distinguish them from non-world cities. Although there is a consensus upon leading world cities, the chosen criteria affect which other cities are included. Selection criteria may be based on a yardstick value (e.g., if the producer-service sector is the largest sector then city X is a world city) or on an imminent determination (if the producer-service sector of city X is greater than the combined producer-service sectors of N other cities then city X is a world city.)
Cities can fall from ranking, as in the case of cities that have become less cosmopolitan and less internationally renowned in the current era.
In 2015, the second Global Economic Power Index, a meta list compiled by Richard Florida, was published by The Atlantic (distinct from a namesake list published by the Martin Prosperity Institute), with city composite rank based on five other lists.