Which cities does Chicago have a real "relationship" with? That is, what cities to we interact with in a special way. It's hard to define, but, to serve as an example, there would not be a special relationship between Chicago and, say, Baltimore?

I'd go with:

New York: the big two in urban structure, of big city feel. a long lasting skyscraper battle and economic competition down through the years

Los Angeles: the whole "who is the # 2 city" in the nation? Lots of Chicago connection with Hollywood. an edgy relationship

St. Louis: Cubs and Cards, of course, but even more so based on Chicago's effect on St. Louis's economic fortunes, the whole reversal of role thing

Detroit: some similiarities with St. Louis. For much of the early 20th century, two cities with so much in common as large, industrial midwestern metropolises. The way the two have gone in different directions since then and the drain that Chicago seems to put on the youth of Detroit who often move here

Minneapolis: Chicagoans recognize it, in some ways, as the midwest's second most forminable city

Indianapolis: somewhat like Milw relationship; tends to be strong because of Chgo influence in IN

Milwaukee: the whole, obvious sibbling relationship, played out with big city and smaller city. Tends to be friendlier than other relationships

Atlanta: Atlanta in many ways tried to become the Chicago of the South. Battle over airports and convention trade spirit this relationship

Boston: This one is wea. I'm sticking this one in strictly because of the Kennedy-Daley family relationship

Las Vegas: strong link for massive numbers of Chicagoans who have gone on trips to Vegas down through the years (supposedly second in size to those visiting from LA); mob link

Phoenix: huge number of Chicagoans who moved there and still retain Chgo roots, causing some desire to recreate Chicago to feel at home (i.e. LEYE restuarants). Cub spring training.

Miami: similiar to Phoenix...lots of Chicagoans retire or have second homes here. Weaker than Miami-NYC link, but has some similiarities

Houston: some similiarities with relationship with Atlanta and with LA (alhtough here its 3 and 4); Houston sees this more as a skyline race between the two than Chicago does

I would agree with most of your summaries, but I don't think the Chicago-St. Louis relationship is completely one-sided. I think there is a reciprocal exchange between the two. I would bet that the largest portion of business travel from St. Louis is to Chicago just based on a lot of people I know and what I hear. But conversely-- and I work in a business-oriented hotel-- a big portion of business travelers to St. Louis are from the Chicagoland area. I think the two cities have always had a pretty important bond. Of course St. Louis doesn't have the same impact on Chicago as the other way around, but there's still an economic benefit to and from both cities.

a few more:

Cincinnati: cities most emblamatic of changing times in midamerica. Cincinnati, the old queen city of the west, was part of the earliest movement west of the Appalachian mts with the Ohio River being the main route and agriculture the region's most important livlihood. This was a migration dominated by the south, particularly VA and made the southern portion of the midwest the most important part of the region. Chicago represented the northern, Great Lakes region, fed by industry, rail, and immigration. This one plays out in MLB with the older NL following the river route for franchises in Pgh and Cin, while the AL came through the region more through the Great Lakes via Cle and Det

San Francisco: although vastly different cities, Chicago and San Francisco alone have the soul of a city in the northeastern corridor. They alone outside the Boston-Washington region offer true urbanity and critical mass. The transcontinental rail road terminated in both ends in Chicago and SF (Oak). Chicago architects were instrumental in the design of SF high rises and bridges. Both cities had the hand of Daniel Burnham (although obviously much more so in Chgo).

New Orleans: important relationship in the NO/StL/Chi/NY jazz pipeline

Pittsburgh: steel,but I find this one to be a very weak link.

I would agree with most of your summaries, but I don't think the Chicago-St. Louis relationship is completely one-sided. I think there is a reciprocal exchange between the two. I would bet that the largest portion of business travel from St. Louis is to Chicago just based on a lot of people I know and what I hear. But conversely-- and I work in a business-oriented hotel-- a big portion of business travelers to St. Louis are from the Chicagoland area. I think the two cities have always had a pretty important bond. Of course St. Louis doesn't have the same impact on Chicago as the other way around, but there's still an economic benefit to and from both cities.
Yeah, but that can be expected when Chicago is the "capital of the Midwest". I'd bet that the majority of business travel to Minneapolis, Indianapolis and Detroit is also from Chicago. It'd still look like a hub & spoke system if you mapped it...

here's another one I missed between Chicago and Boston: that whole Wrigley/Fenway/Cub/Red Sox/curses/lack of WS rings/rabid fan thing. It really was a nice link but the Red Sox sure screwed up last October. Anway, it's still a link between the two. I suppose, keeping the MLB theme, "Sox" is another one.

How about:

Chicago and Winnipeg: Winnipeg has a lot of Chicago school architecture, and is also a major train, road, and cultural midway between East and West. Both have agricultural exchanges.

Chicago and Toronto: Both have had renaissances that have resulted in economic, cultural, educational, political, and social surges. I think in some ways Toronto sees Chicago as its bigger, stronger sister city with some similar social and growth patterns.

New York, Toronto and LA