* How government is setup, in some countries (and in some areas of countries) many things are done at the city level, others bump a lot up to county, state, or even country government. The USA manages schools at the city or below, and so city boundaries become well-fought over.
Whenever you see "Unified" you're seeing something built out of smaller, usually city-related, parts.
* Age of the city
* Natural boundaries (rivers, mountains)
* How government is setup, in some countries (and in some areas of countries) many things are done at the city level, others bump a lot up to county, state, or even country government. The USA manages schools at the city or below, and so city boundaries become well-fought over.
Whenever you see "Unified" you're seeing something built out of smaller, usually city-related, parts.