This comic from Emily McGovern at Emily's Cartoons sent me down an internet wormhole, but I learned a few things. Hogwarts School of Witchcraft and Wizardry is indeed in Scotland. And indeed, it makes no sense that students from Scotland would have to travel to London to catch a train to school. But as the wiki states, "The precise location of the school could never be uncovered because it was rendered Unplottable." Maybe the roundabout route for Scottish students is a way of keeping the location a secret, you think? That may be it. The Hogwarts Express train was inaugurated in the 1850s as a way to transport students to the school without drawing the attention of Muggles.
Could a parent in Scotland just drive their student to Hogwarts? No. According to the wiki, "the Ministry decreed that students would arrive to school on the train or not attend at all." Just like Muggle schools, there are rules that don't make sense. But a dedicated train doesn't conceal the fact that on September first, a large contingent of schoolchildren arrive at Hogsmeade Station in Scotland and are whisked away to the school. Apparently, the folks in Hogsmeade do not travel all that much. Check out McGovern's Tumblr site, where you'll find a substantial series called My Life as a Background Slytherin. -via Geeks Are Sexy