Geographical segregation exists whenever the proportions of population rates of two or more populations are not homogeneous throughout a defined space. Populations can be considered any plant or animal species, human genders, followers of a certain religion, people of different nationalities, ethnic groups, etc.

In social geography segregation of ethnic groups, social classes and genders is often measured by the calculation of indices such as the index of dissimilarity. Different dimensions of segregation (or its contrary) are recognized: exposure, evenness, clustering, concentration, centralization, etc. More recent studies also highlight new local indices of segregation.

Geographical segregation is most often measured with individuals' place of residence, but increasing geographical data availability makes it now possible to compute segregation indexes using individuals' activity space, in whole or in part.

Segregation, as a broad concept, has appeared in all parts of the world where people exist—in different contexts and times it takes on different forms, shaped by the physical and human environments. The spatial concentration of population groups is not a new phenomenon. Since societies began to form there have been segregated inhabitants. Either segregated purposefully by force, or gradually over time, segregation was based on socio-economic, religious, educational, linguistic or ethnic grounds. Some groups choose to be segregated to strengthen social identity.

Segregation can be caused by legal frameworks, such as in the extreme example of apartheid in South Africa, and even Jewish ghettoization in Germany in the 20th century. Segregation can also happen slowly, stimulated by increased land and housing prices in certain neighborhoods, resulting in segregation of rich and poor in many urban cities. Segregation can also be assigned arbitrarily. This can occur on a global scale, such as is seen in the Partition of India, instances in Ireland, and many other situations. Geographical boundaries were often put in place without much consideration for native peoples and natural geographic terrain and cultural limits that had long been in place.

In the United States, segregation was enforced through the law. Notably, the racial segregation between white and black racial populations in the American South during the late 1800s into the first half of the 20th century. These laws consisted of separating people of color from white people in public places, including movie theaters, restaurants, schools, shopping centers, etc. The legislations were commonly referred to as Jim Crow laws. Although these laws were abolished in the mid 1960’s the impacts are still present in American communities today. Represented through the significant gap in homeownership, income status, and education levels in communities of color versus majority white.  

In apartheid South Africa, segregation was very much a legal concept. Enforced by the government, black and South-Africans of color were discriminated against, and forced to comply with apartheid. Some of the legislation passed dealt with physical segregation in schools, land tenure, geographic segregation and state repression. These were very clearly legislative, but also in the case of most white South Africans, a social construct as well.

Segregation can also be encouraged, using geographical boundaries, while not explicitly enforced. Public housing projects, especially in the United States, have been criticized for this. Putting cheap housing in poor black neighborhoods encouraged local African-Americans to stay in the area, keeping other richer areas white by not building public housing there. Current day, many communities within the United States are still segregated, due to the ongoing racial inequalities still present and self-segregation.