The origins of frost point to logical methods of avoiding it. The first is to plant on slopes from which surface-chilled air can drain away freely (see air drainage). Free-standing and projecting hills are best because they have no external sources of chilled air and what slips away must be replaced from the warmer atmosphere above (see topography). This is the most effective form of frost protection, but typically is generally an option only when developing vineyards in new regions that allow such vineyard site selection.