Hann is fairly insignificant in world terms, it sits at the bottom of the Western Continent between Oerth and Maztica, and has the same sort of weather as Spain or Northern Italy would expect in the real world. The Eastern Continent includes Kata Tur, Zachara and the Wild Lands.
Greater Hann used to be a single High Kingdom composed of a number of minor Kingdoms and Principalities scattered around a huge mountain range. The Greater Kingdom of Hann has subsequently been destroyed by invasions from hordes of barbarians and monsters from the mountains or from the Grand Caliphate of Zachara. All that remains are a number of independent states who are held loosely together by Oliver Green-Barrell, Raven King of Armes of the College of Heralds. The main areas are The Strongholds, The Great Lake States, Razadi, The Far Coast States, Galinia & Angasa, and The Holy Isle.
The College of Heralds chronicle the history of the Greater Hann area and maintain the calendar, as well as recording noble estates and maintaining The Honours System.
I tend to play a mixture of 1st and 2nd edition AD&D rules, with a number of House Rules thrown in for good measure. The current game is based in the Galinia region and is run over the internet at PlayByWeb.