The metropolitan areas of San Diego, California, and Tijuana, Baja California, together form an international conurbation that crosses the USA-Mexico border at the northern end of the Baja Peninsula near the city of San Ysidro. In this photograph taken by an astronaut on the International Space Station, urban and suburban areas appear light gray, speckled with white rooftops that indicate large industrial and commercial buildings. Vegetated areas -- parks, golf courses, and the foothills of nearby mountains -- appear green, in contrast to the tan and dark brown of exposed soils and bedrock in highland areas.