A global city (also known as a power city, world city, alpha city, or world center) is a city that serves as a primary node in the global economic network. The concept originates from geography and urban studies, based on the thesis that globalization has created a hierarchy of strategic geographic locations with varying degrees of influence over finance, trade, and culture worldwide. The global city represents the most complex and significant hub within the international system, characterized by links binding it to other cities that have direct, tangible effects on global socioeconomic affairs. The criteria of a global city have varied over time and depending on the source; common features include a high degree of urban development, a large population, the presence of major multinational companies, a significant and globalized financial sector, well developed and internationally linked transportation infrastructure, local or national economic dominance, high quality educational and research institutions, and a globally influential output of ideas, innovations, or cultural products. Quintessential examples, based on most indices and research, include New York City, London, Paris, and Tokyo. Origin and terminology The term global city was popularized by sociologist Saskia Sassen in her 1991 book, The Global City: New York, London, Tokyo. Prior to that, various other terms were used to describe urban centers with approximate features. The term world city, meaning a city heavily involved in global trade, appeared in a May 1886 description of Liverpool, by The Illustrated London News; British sociologist and geographer Patrick Geddes likewise used the term in 1915. The term megacity entered common use in the late 19th or early 20th century, with the earliest documented example being a publication by the University of Texas in 1904. In the 21st century, the various terms are usually focused on a city's financial power and high technology infrastructure, with other factors becoming less relevant. Criteria 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 on the 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 is a world city) or on an imminent determination (if the producer-service sector of city is greater than the combined producer-service sectors of other cities then city is a world city.) Cities