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Size: Michael's area encompasses about 50,000 square miles, which is about equivalent to Alabama or Arkansas or just a bit smaller than Michael's native Iowa. Going by country, this is close to Greece, twice the size of Ireland or twice the size of Lithuania. This is a rough calculation, using the size of the Wall as a measurement, and assumes that the official map of Westeros is to scale.
People: In Michael's territory, there is currently 35,000 people, spread out among his land, but mostly concentrated on the coast and along other Lord's territories.
Resources and landscape: The land has a large mixture of different geological zones. The northern coastal (NC) region is forested and includes a large variety of different trees (though it has no Ironwood). The northern interior (NI) has plenty of mountains and lakes (including the Twin Lakes) and has a variety of different resources available. Some are known to Michael and the Starks from historical data, and some are yet to be discovered. There are several smaller coal and iron mines that are already noted but were never seriously excavated for economical reasons. The southern coastal (SC) region is incredibly rocky, but fairly flat feature wise. Most trees were long ago cut down, and most of the land is only good for grazing. There is very good fishing along the coast. The southern interior (SI) is forested in its northern portion (similar to the NC region) but opens up to plains (with plenty of rivers and streams) as it approaches the Twin Lakes River. There is plenty of rivers in this area as runoff from the mountains.