Thanks for the map - Should point out for non Perthies - The housing estates up there are not confined to the coastal strip which lies between the now 4 lane Marmion Ave to Yanchep and the beaches. New Estates are appearing east of Marmion Ave and the to be Perth- Yanchep railway line.
It looks like the Yanchep National Park may constrain some development at Yanchep but that is years away.
Also Yanchep is not the furtherest the population has spread - Two Rocks is further North from Yanchep but is currently small and is on the edge of the Crayfishing areas up the coast.
One final point, various State Govts have looked into the future and as a result that region within 3/6 years will be served by the Mitchell Freeway and the Perth-Yanchep railway. The region just cannot be ignored - It will be in the future too big to overlook.