Setting can tell you just about everything you need to know in this movie, since the three major locations Charles Kane lives in mark the three stages of his life. The first stage is his boyhood in Colorado, which we only get a brief glimpse of. In his younger years, Charles lived in poverty in Colorado, a state that represents the wild freedom of Charles' young life. Unfortunately, his parents tell him "This ain't the place for you to grow up in" and he moves away to live with Mr. Thatcher in New England.
Charles never has any money in Colorado, but he doesn't seem to care because he has an active imagination and a lot of love for his mother.
Charles' life changes forever when he leaves Colorado for New England. This shift marks Charles' fall from childhood innocence into the world of glitz, glamour, and money. By the time he's forty, Charles has already gone through a major scandal while running for governor of New York. His fast-paced life has led him to hurt a lot of people and lose a lot of friends. If only he'd never left Colorado, he might have even had a shot at being happy.
When Kane loses his New York newspaper and gives up on his wife's singing career, he leaves New York in shame and moves down to his new gigantic mansion in Florida. This is the place where he lives out the rest of his days in isolation. Even his wife Susan leaves him because she can't bear to be so cut off from people. As she says, "Forty-nine thousand acres of nothing but scenery and statues. I'm lonesome."
(P.S. Notice that the mansion is a barely disguised version of Hearst Castle in San Simeon, California. This is...not a coincidence.)
There you have it, folks: we can chart Kane's character arc by where he is geographically. He moves from his family home in the West (which often symbolizes hope) to New York City (which, for good reason, often symbolizes corruption and greed) to isolation in Florida (which, well… we love the Sunshine State and all… but it is often synonymous with some pretty weird and bleak goings-on.