I disagree with this statement:
every migration includes an immigration and an emigration
Note this definition from Wikipedia:
Emigration is the act of leaving one's native country with the intent
to settle elsewhere. Conversely, immigration describes the movement of
persons into one country from another. Both are acts of migration
across national boundaries.
Especially for large countries such as the United States, Canada, Australia, there can be plenty of things to research about migration which do not involve finding explicit emigration/immigration records. If we cannot use migration to tag movement within country boundaries, what should we use instead?
The situation is complicated further by the fact that what we call "immigration records" -- e.g. passenger lists required by the US Federal Government to collect data about immigration -- actually contain a great deal of information about the arrival of people who are NOT immigrating -- US Citizens returning home, lists of crew working on the ship, and people coming to the USA who had no intention of making permanent residence here.
I believe there should be three separate tags.
- emigration for questions about people leaving their home country
- immigration for questions about people entering a new country
- migration for questions about the routes taken by individuals and families because of historical events (the pull & push factors, possible modes of travel, how the geography of an area affects the movement of people, etc.)
In this answer vervet says:
My only issue is that it is often hard to say which tag should be used.
If that is the case, it may be a sign that the question is broad, and could be broken down into multiple questions, or that other tags might be more useful.