Why are enclaves or enclaves created?

An enclave is a piece of land which is totally surrounded by a foreign territory. An exclave is a piece of land which is politically attached to a larger piece but not physically coterminous with it because of surrounding foreign territory. Many entities are both enclaves and exclaves.

Geologists use  seismic waves to  locate an earthquake's epicenter.. 

Nation of conflicting ethnic groups