Topographic map of the Earth's surface. Yellow, orange, and red colors represent progressively higher elevations; green, light blue, and dark blue represent progressively lower elevations. The middle of the Atlantic Ocean (see closeup map below) contains a topographic high (light blue curvilinear feature) surrounded by the deep ocean (dark blue). This feature is the Mid-Atlantic Ridge, and marks the boundary between the North American and European or South American and African tectonic plates. Images from NOAA's National Geophysical Data Center.