The chief doorways of the world of international commerce are its harbours and ports. Through them pass cargoes and travellers from one part of the globe to another. A harbour is any sheltered body of water where boats or ships may moor or anchor. A port is an installation that has been built around a harbour with facilities for loading and unloading such vessels.
Ports are classified according to the types of traffic which they handle. An industrial port specialises in bulk cargo--grain, sugar, ore, oil, chemicals, and similar materials. A commercial port is one which handles general cargo--packaged products and manufactured goods, for instance--as well as passenger traffic. Comprehensive ports handle bulk and general cargo in large volume. Most of the world's great ports are classified as comprehensive.
The development of a harbour into an economically thriving port depends upon several basic conditions. The contiguous land areas should be suitable for piers, wharves, loading and unloading facilities, and warehouses. The surrounding region should be geographically favourable to the development of a population centre and supporting industries, such as railroads and ship repair. There should be an accessible interior which furnishes products for export and provides a market for imports.
River dredging and canal construction have made inland cities into seaports. Manchester, England, is connected with the sea by the Mersey River and by a 35-mile canal, so steamers may unload cargoes directly into the city's mills. Hamburg, Germany, 75 miles from the North Sea, is a major port because continuous dredging has deepened the Elbe River channel. Houston, Tex., is linked with the Gulf of Mexico by means of a ship canal.
Chicago, whose port is used mainly for Great Lakes shipping, also handles cargo via a dredged tributary to the Mississippi River. The completion of the St. Lawrence Seaway in 1959 made every port on the Great Lakes available to ocean-going vessels. This was made possible by dredging shallow sections of the waterway to a minimum depth of 27 feet.