Wikipedia:

A global city (also called world city or sometimes alpha city or world center) is a city generally considered to be an important node in the global economic system. The concept comes from geography and urban studies and rests on the idea that globalization can be understood as largely created, facilitated, and enacted in strategic geographic locales according to a hierarchy of importance to the operation of the global system of finance and trade.
Also factored into this rating system is a city's political and cultural importance (in that order: culture is last, economy first—neoliberalism rules everything around me). So, where is Seattle in this order of things? At the middle of the middle. Vancouver, of course, beats us; Portland, of course, does not.