The last frontier for development in York Region essentially exists north of the Oak Ridges Moraine, which runs east-west through the centre of the region. Virtually all the land south of the Moraine is urbanized (Town of Markham, City of Vaughan, and Town of Richmond Hill). To the west, the wide, deep valleys of the Humber River act as major constraints in northern Vaughan, while the heavily rural Township of King has maintained several large blocks of forest and significant wetland (Figure 6). To the east, in north Markham, there is a narrow (3 to 4 km wide) band of farmland remaining south of the Oak Ridges Moraine, much of which is already owned by development interests.
North of the Moraine, through the Towns of East Gwillimbury and Georgina, there are large areas of unserviced rural land, although historically, residential development has been concentrated in the Lake Simcoe communities of Keswick and Sutton. Further inland there are a number of large swamp wetlands associated with the major creek systems that drain northward to Lake Simcoe, including the Holland River, Black River, and Pefferlaw Brook. All of these are provincially significant wetlands that preclude any form of development. Those few sections of the south shore of Lake Simcoe that are not already developed are constrained by clay soils with high (perched) water table conditions and large patches of second-growth woodland.
In its Official Plan, York Region (1999) identifies a Greenlands System (Gartner Lee Limited 1994) that recognizes and protects ecologically significant/sensitive areas such as ESAs, ANSIs, wetlands, and large forested areas (Table 5).