The Continental Divide is more than the cartographic line that runs along the crest of the continent, marking where a drop of water falling on one side flows to the Atlantic Ocean, and on the other, to the Pacific Ocean. It is a historical, cultural, and conceptual space as well. All lines that divide things are also, by definition, places where things meet, like a seam. In this way, an examination of the line, between Canada and Mexico, is a journey that looks at a common territory, along the shared space of divergence, where the shape of one thing defines the shape of the other.