The Chicago of "Chicago" is a hustling, bustling, building, breaking, rebuilding kind of place. The city is being built, torn down, and rebuilt as we read it. It's a crazy place of freight trains, construction workers, and all kinds of laborers. We'd go as far as to say that the poem is dominated by industrial imagery—imagery of work, toil, building, and technology. Chicago is in the middle of the expanding nation (remember, the poem was written in 1914) and Sandburg puts us right in the middle of all that hub-bub. We can almost feel the freight trains whooshing by.
Lines 1-3: The speaker describes Chicago as a manual laborer. It's a hog butcher, took maker, a stacker of wheat. It's also described as an industrial laborer—it's a "player with railroads and the nation's fright handler." It's located right in the middle of all that exciting industrial action.
Lines 10-11: Chicago is portrayed as proud of all its strength and cunning. We feel the "toil" in these lines, and we also find out that not every city is like Chicago. Out city is a particularly tough and industrializing place.
Lines 13-17: Here we have a long list of adjectives describing the action of the city. It's being built and rebuilt. We feel like we're in the middle of a construction site in these lines, as buildings reach towards the sky all around us.