Oceans and Seas
Oceans and seas are large bodies of salt water. The difference between the two is that a sea is smaller than an ocean, and is generally surrounded by land.  The four oceans are the Atlantic, the Pacific, the Indian, and the Arctic.  An example of a sea would be the Red Sea which lies between Africa and Asia in the Middle East.

Oceans and Seas have positive and negative effects on human civilization.  They often act as a barrier to both cultural diffusion and invasion.  However, many civilizations developed good sea travel and were able to overcome this effect.  Great Britain, Portugal, Spain, Greece, the Roman Empire, the Netherlands, Early China, and Japan all were major naval powers at one time or another. In fact, for many of these civilizations, oceans and seas acted as highways of trade, cultural diffusion, and invasion.  Oceans and seas also provide a rich source of food and other resources, such as minerals and oil.  Many of the above mentioned cultures developed major fishing industries as a way to feed their populations.  Countries like Japan have a diet composed mainly of sea products and farmed vegetables.  Great Britain, in the twentieth century, began drilling for undersea oil off the north shore of Scotland.  Today, this valuable resource provides much of their energy needs.

Peninsula
A peninsula is an area of land surrounded on three sides by water. Italy, Greece, and the southern part of India are all peninsulas.  The advantages and disadvantages of living on a peninsula are the same as living in any coastal region.
 

Isthmus
An isthmus is a narrow stretch of land connecting two larger areas of land.  Panama in Central America is an isthmus. The advantages and disadvantages of living on a peninsula are the same as living in any coastal region.
 

Strait
A strait is a narrow stretch of water connecting two larger bodies of water.  Examples would be the Strait of Gibraltar connecting the Atlantic Ocean to the Mediterranean Sea, and the Strait of Magellan, which is at the tip of South America, connecting the Atlantic Ocean and the Pacific Ocean.  Straits are strategically important due to the control of trade or control of military access to a specific area. Controlling the Strait of Gibraltar means controlling access in and out of the entire Mediterranean Sea until the building of the Suez Canal on the Red Sea.
 

Regular Coastlines
A Regular Coastline is smooth with very few natural harbors.  Africa is an example of a regular Coastline.  Regular coastline make building ports and harbors very difficult.  Without these, trade, sea travel, and cultural diffusion are near to impossible.  But, this also prevents invasion from the sea.  This feature of Africa kept invaders out of sub-Sahara Africa for millennia.
 

Irregular Coastlines
An Irregular Coastline is not smooth, and has many natural harbors.  India is an example of a irregular coastline.  This feature makes the development of ports and harbors much easier, allowing trade, sea travel, and cultural diffusion to occur. But, it also allows for an easy invasion route.  India has suffered through centuries of foreign domination due to its easy access by sea.


 

Islands/Archipelagos
An Island is an area of land completely surrounded by water.  Examples include Iceland, Great Britain, and Madagascar.  Islands often lack many natural resources and are forced to trade with other nations.  Most island nations develop good forms of sea travel, such as Great Britain and Japan.  Throughout history islands have been used as stepping stones to cross the major oceans.  The Pacific Ocean is full of Archipelagos, which are chains of islands.  Japan is a prime example of an archipelago.  Most archipelagos have irregular coastlines which make them vulnerable to invasion, but also foster trade and cultural diffusion.  The many archipelagos in the Pacific helped spread civilizations from the Asian mainland, and would much later help European explorers circumnavigate the globe.