America, second largest isolated landmass of the earth, comprising the two continents of the western hemisphere. America is a common designation for either or both North America and South America, for the western hemisphere as a whole, and for the United States of America. The entire western hemisphere is often called the Americas. The word first appeared in Cosmographiae introductio (Introduction to Cosmography), edited and published in 1507 by the German cartographer Martin Waldseemüller. The name was derived from Americus, the Latinized given name of the Italian navigator Amerigo Vespucci, whose expeditions to the New World are described in the work. As used by Waldseemüller, America specifically referred to the lands discovered by Christopher Columbus, Vespucci, and other early explorers of the West Indies and the northeastern coast of the southern continent. The Flemish geographer Gerardus Mercator first used the word to indicate all the western hemisphere on a map of the world published in 1538.
Central America, region of the western hemisphere, made up of a long, tapering isthmus that forms a bridge between North and South America. Central America, which is defined by geographers as part of North America, has an area of about 521,500 sq km (about 201,300 sq mi) and includes the countries of Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama. The region has a population of approximately 36.4 million (2000 estimate).
II THE NATURAL ENVIRONMENT
In strictly geological terms, Central America begins at the narrow Isthmus of Tehuantepec, in southern Mexico. That narrow section divides the volcanic rocks to the northwest from the folded and faulted structures of Central America. The southernmost geological limit of Central America is the Atrato River valley, in Colombia, South America, just east of the Panama border.