A couple weeks ago I was hiking with a few brothers in the Blue Mountains when maghrib set in. Alhamdulillah the brothers decided to pray on time, but there was not enough suitable space to pray in congregation. I informed my son to pray shortened, as we were travelling, but a few of the other brothers decided to pray full. This sparked a debate about where the limits of Sydney are. One of the brothers said the Blue Mountains are part of the "Greater Sydney Basin," and therefore one should pray full. I felt that the Blue Mountains were outside of Sydney but had to do my research.
Knowing when one becomes a traveler according to Islamic Law is of great importance. One must shorten their 4-rakaat prayers to 2-rakaat and one cannot fast while travelling. To learn more about the rules of traveling click on Sayyid Sistani or Sayyid Khameni.
There are some general rules when it comes to locating starting point for travel. Some scholars in the past considered one's house or one's neighbourhood (e.g. Kingsgrove) as the starting point. But, the mainstream scholars of today have determined the borders of the city where one lives is the starting point. Then, from the starting point one must travel 44-45 kilometres round trip, hence one's prayers are shortened and one cannot fast at the 22.5 kilometres mark from the border of the city. Therefore, it is important to know where the borders of a city are to determine where the travelling point is.
According to this map found on Sydney's Wikipedia page, the border to the west is Emu Heights and Leonay. Therefore, one would have to calculate 22.5 kilometres past this point, which would be located between Faulconbridge and Linden. Towards the south, the border is Waterfall and 22.5 kilometres past Waterfall is about Thirroul if one is travelling on the M1. Finally, towards the north, the border is the Brooklyn Dam and 22.5 kilometres past Brooklyn is right before Kariong. Hopefully this helps those living or travelling in Sydney.