Medellín, officially the Special District of Science, Technology and Innovation of Medellín, is the capital of the department of Antioquia, and the second-largest city in Colombia after Bogotá. It is located in the Aburrá Valley, a central region of the Andes Mountains, in northwestern South America. The city's population was 2,427,129 at the 2018 census. The metro area of Medellín is the second-largest urban agglomeration in Colombia in terms of population and economy, with more than 4 million people.