Alaska and the African Jungle both represent the same concept in Death of a Salesman. Willy associates these places with his brother, Ben, a self-made man who achieves his success in the wild.
Ben is Willy's model for success and significant achievement. When Willy imagines what success looks like, he pictures his brother. Notions of personal greatness and truly vast potential for personal gain play into Willy's view on the exotic places where his brother grew rich.
Importantly, Willy maintains a strictly romantic (and vague) notion of how his brother actually gained his wealth in Alaska and Africa. In his imagination, Willy repeats his last visit with Ben.
Ben remarks: "William, when I walked into the jungle, I was seventeen. When I walked out I was twenty-one. And, by God, I was rich!"
The setting for Ben's adventures are so foreign to Willy that they are dream-like. Alaska and Africa belong to the same vaguely defined dream that Ben does, for Willy, and so represent an adventurous way of life marked by boldness and easy money.
Part of Willy's fixation on success, these places function as yet another reminder for the audience that Willy only dreams of success and does not actually strive for it. He resents his failure, but his ideas of success are as vague as his image of the wilds of Africa and Alaska.
The American West is not a strong symbol in Death of a Salesman. Biff returns from his time on a ranch in the west, but that place, for Biff, is not related to success and stands instead as a failure.