Your Electorate of Willoughby is on the North Shore of Sydney, and is 26 square kilometres in size.
The electorate of Willoughby covers the suburbs of Artarmon*, Cammeray, Castlecrag, Castle Cove, Crows Nest*, Chatswood, Chatswood West, Lane Cove North, Middle Cove, Naremburn, Neutral Bay*, Northbridge, North Cremorne, North Sydney*, Roseville*, St Leonards* and Willoughby. The postcodes included in the Willoughby Electorate are 2060, 2062, 2063, 2064, 2065, 2066, 2067, 2068, 2069, 2089, and 2090.
You can find a more detailed map of the Electorate of Willoughby here. The Australian Bureau of Statistics also has some useful information.