SR4 tried to take the game to a more globetrotting style. the idea being "it's a small world" and all that. It's had a mixed reception from fans, overall. Some love it and their characters hop from place to place. Others like to keep the game enmeshed in a single location, whether it's Seattle, Berlin, or somewhere else.
Seattle is the home of Shadowrun though, and is designed as the ultimate Microcosm, where you have examples of everything from throughout the 6th world bottled up in one location, so Shadowrun always comes back to Seattle.
Runner Havens, a now out of print sourcebook, was one of the first sourcebooks released for SR4, and it covered Seattle and Hong Kong (plus had short write ups on a few other locations). And then for Shadowrun's 20th anniversary, a hardcover sourcebook, Seattle 2072, was released, a full blown update of Seattle, somewhat old SR1 Seattle Sourcebook style.
As for adventures... For published stuff, the first part of Ghost Cartels takes place in Seattle. A Fistful of Credstick, the fist Horizon Adventure is set in Seattle. Anarchy Subsidized, the second adventure starts in Seattle, but moves to Neo-Tokyo,
Also, Season 4 of Shadowrun Missions is set in Seattle. We have 8 Adventures in the Season 4 series out so far, with more incoming.
Bull