From the very beginning, one of the most magical things about Harry's world has been its proximity to our own. We love to think that if we just look closely enough, we might notice that our wacky next-door neighbor seems to wear these crazy robes all the time and has trouble using household appliances… Any evidence that wizards are out there, practically living alongside us mere Muggles, could be enough to believe that Harry is real, and so is magic. Fine by us!
And, in staying so close to our own realm, we witness both the Wizarding world and the Muggle world start to collapse a little bit here, with Voldemort's plans to basically enslave the Muggles (that is, us) under wizard domination. Unbeknownst to them, Voldemort poses as much a threat to Muggles as he does to the wizarding world.
In keeping with this dominant sense of danger, the setting of this book is hard to pin down – if anything the "setting" of most of Book 7 is constant movement. Sure, Harry, Ron, and Hermione touch upon a few significant places in their journeys – notably, the infiltration of the Ministry of Magic, Harry's mournful homecoming to Godric's Hollow, and the brief and restful stay at Bill and Fleur's home, Shell Cottage. But, for the most part, the first three-quarters of the book are marked by our trio's never-ending flight.
However, the book, like Harry and Voldemort, comes "home" in the end, to the one place that's central to all of the books – Hogwarts. It's fitting that the book and the series as a whole should end with our hero and our nemesis facing off at Hogwarts; the school is the only real home that both Harry and Voldemort have ever known. And, in a way, since we see things through Harry's eyes, it's the only home in the books that we, his readers, have ever known, too. Rowling's novels take us on journeys through many magical, weird, and wonderful places – but, in the end, it's always Hogwarts that remains the beacon of the wizarding world and of Harry himself – a symbol of learning, acceptance, companionship, and loyalty.
One brief note on the chronology – according to author J.K. Rowling, the timeline of the books have them take place in real time in the 1990s, based on when she started writing the book in 1990. The events of Harry Potter and the Deathly Hallows thus fall in 1997 and 1998.