Stretching across approximately 8,500 acres, North Irvine is planned to achieve a balanced and sustainable mix of permanent open space, a range of housing opportunities and business centers. It includes five General Planning areas - 3, 6, 9 and portions of 5 and 8. The Northern Sphere Planning Area includes the city of Irvine's General Plan Planning Areas 3, 6, 9 and portions of Planning Areas 5 and 8, generally bounded by Trabuco Road and by the former El Toro Marine Corps Air Station to the south, Jeffrey Road and existing residential development to the west and the Santiago Hills to the north. The Foothill Transportation Corridor (SR-241) traverses the northern portion of the site.