The important things to consider when creating a game environment are: Terrain and Weather, Flora/Fauna, Resources, Races and People, Cultural Overview, Calendar and Holidays, Standards of weights and measures, Institutions (Religions, Governments, Guilds, Large Businesses), Laws and Morals, Family life, Social Classes, Political, Economics, Religion, Technology, Transportation, Arts/ Literature, Shadow (Criminals and those in the shadows of society), Power (Magik, psionics, etc), Paranormal (beasties, monsters, etc), History of the area, and Rule Modifications to accommodate the game environment.
Each game environment be it a continent, country, city, temple, village, or dungeon/ place of adventure, needs these areas addressed.
Any "sub area", a smaller region in the larger one, needs to keep the larger area's answers in mind.