From Simpsons Wiki

Capitol City is the capital of the state where Springfield is located. The city nickname is "The Windy Apple" (a portmanteau of The Windy City and The Big Apple). Principal Seymour Skinner was born in the city, and Milhouse Van Houten's mother, Luanne Van Houten, briefly moved there after her divorce.

The city is 220 miles away from Springfield, with air-routes, several roads, and a railway linking the two cities. The city also has several large hotels which frequently host conventions attended by the Simpson family, and Capital City also hosted the Super Bowl and the music festival Hullabalooza.

Origins

It is believed that the true inspiration for Capitol City comes from the city of Portland, Oregon. Since Matt Groening is from Oregon, many Oregonians believe that the city of Springfield in the series is taken from Springfield, Oregon, thus making Eugene, Oregon the inspiration for neighboring city Shelbyville, and making Portland the inspiration for Capitol City. It is also a known fact that many of characters in The Simpsons are named after streets in Portland (i.e. Reverend Lovejoy, Ned Flanders, and Monty Burns, for Burnside.)

Events

The city is often host to major events such as concerts, sports games and United Nations Conferences. It has its own major league baseball team, The Capitol City Capitals, with mascot The Capitol City Goofball. Other attractions include the Crosstown suspension bridge (Portland is also known as Bridgetown, for its many bridges over the Willamette River), the main Duff Brewery (inspired by the Henry Weinhard's brewery in Portland), the Capitol City Stadium, the Capitol City Amphitheater and the intersection of 4th and D streets (Broadway and Burnside Streets in Portland.) Boxer Dredrick Tatum grew up in the "projects of Capitol City."

The city has its own version of Monopoly, which Milhouse brought Bart after returning to Springfield. As described by Milhouse, "Baltic Avenue is now Wayne Street, It's awesome!"

Landmarks

Landmarks and stores in Capitol City featured on the show include the Bootleg T-Shirt Emporium (inspired by Portland's Saturday Market), Capitol City Plaza Hotel (where Homer Simpson and Mindy Simmons stayed during the National Energy Convention), Duff Brewery, Madame Chao's Chinese Restaurant, St. Dominick's Cathedral, The Penny Loafer, Volkswagen World, and the 2nd Best Western Hotel.