As "The Geographer" at the National Geographic Society, it's Alex Tait's job to know a lot about maps. Alex guides us through the streets of Washington, D.C., United States, using geography to show the evolution of our nation's capital. From boundary stones placed in the 1790s marking off the city's distinctive diamond outline to the modern-day Metro system, Alex shows us why Washington, D.C., looks and feels the way it does today.