There are four property colors that represent different terrain types, e.g. green = forest. The more a player invests in the property to "level it up" (ala adding houses or a hotel in "Monopoly"), the more the terrain flourishes (e.g. forests become more dense with trees). This then provides additional defense to creatures of the matching color type, and exacts a higher toll on opponents landing there. And as a player collects more lands of the same color (creating "chains") the tolls, as well of the land values, increase.