Needs removing. Base trait Isthmus. Generally this will be used for Isthmuses, but it can be used for any HCen and HSep terrain that fits the geometry.
Sets the HCen terrain. Sets the two opposite HCorners and sets the four HSep terrains adjacent to the pulled in vertices. The HSep terrains can be different on either HSep of the isthmus. For eample it could be sea on one HSep and fresh water lake on the other.
Sets the HCen terrain. Sets the two opposite HCorners and sets the four HSep terrains adjacent to the pulled in vertices. The HSep terrains can be different on either HSep of the isthmus. For eample it could be sea on one HSep and fresh water lake on the other.