"Chicago" is filled to the brim with personification. By the end of the poem, Chicago seems to be way more like a man than like a city. It has shoulders, a heart, a pulse, and it laughs (and laughs and laughs). What's the reason for all this personification? Well, Sandburg paints a portrait of a city that is, in some ways, very human. It's flawed and it's beautiful, it's rough-and-tumble and intense. It's vibrant and multi-faceted. It turns out that the best way for Sandburg to comprehend the city is to compare it to a human being—that way, we have a tangible frame of reference for all the beautiful, strong, messiness.
Lines 1-5: Here, the city is described as various types of workers; it is a hog butcher and a tool maker and so on. The city resembles the very people who live in it.
Lines 6-8: The city is described as "wicked," and "crooked" and "brutal"—this city sounds like a not-so-nice person.
Lines 10-12: Here the speaker defends the city, and refer to its "lifted head singing so proud to be alive and coarse and strong and cunning." This city is ALIVE, by gum, and that's what matters. The speaker even goes so far as to compare Chicago to a tough-acting baseball player.
Lines 18-23: The speaker continues his description of the city, and imagines that it even has a body, a pulse, and a heartbeat. And, Chicago laughs a deep throaty laugh in pride. By the end of the poem, we feel like we could reach out and touch this muscle-y tough guy.