What is an example of a cultural boundary?

There are different kinds of cultural boundaries. It could come in the form of a religious, ethnic, or language boundary.

Religious: When Britain partitioned India and created Pakistan, it created a religious cultural boundary. Muslims were reorganized into Pakistan and Hindus into India.

Another example is in Ireland with the UK Protestants in the North and Roman Catholics in the Republic of Ireland.

Language: Most examples come from Europe. France, Spain, Portugal, etc all based their boundary lines because of the language people spoke.