SimCity

SimCity is the city in which all of the games in The Sims series are based and is a major city in SimNation. Many products and services come from SimCity. Buy Mode items are also apparently made there as well. The city is apparently a global city.

The Sims era
In The Sims, The Sims for console, and The Sims Bustin' Out for console, the newspaper is called "SimCity Times," and many services are labeled "SimCity." In The Sims: Hot Date, the main stretch of community beach is named "SimCity Beach," implying that Downtown is part of SimCity. Also, when first loading The Sims: Unleashed, Old Town is described as "SimCity's new historic Old Town district," which confirms that Old Town is part of SimCity. As Magic Town and Vacation Island are separate from the city, and it can be debated for Studio Town, it can be concluded that Neighborhood 1, Neighborhood 2, Old Town, Downtown, and SimValley are districts/suburbs of SimCity.

The Sims 2 era
In The Sims 2, the newspaper and many city services and agencies are labeled "SimCity." This seems to indicate that the Neighborhood is in or directly adjacent to SimCity. While it is debatable for other neighborhoods such as Veronaville and Strangetown, Pleasantview is definitely a part of the city. In The Sims Pet Stories, Arbor Falls is mentioned to be nestled in the mountains of SimCity.

Politics
The Politics career in The Sims and The Sims 2 describe SimCity as being the State Capital where the State Assembly is held. The state can be inferred as being Sim State, due to the name of Sim State University and it's proximity to the city (if as assumed, the university is part of SimCity). It is never mentioned if it is the National Capital, or if it follows a similar structure to the United States by having the Capital as a city that is not in any state like D.C.