Perth is a very isolated city.  In fact, that is probably an understatement.  Short of Honolulu, Perth is probably the most isolated major city on the planet.  It’s closer to many major cities in Indonesia than it is the main cities on the Eastern Seaboard of Australia.  With that in mind, it’s exceedingly rare to see an aircraft’s vapour trail in the sky, as almost anything that flies near Perth has to land here and therefore the planes aren’t at a sufficient altitude for there to be vapour trails above the CBD.  The above image adds to about four that I’ve seen in the three years I’ve lived here.
City Beach, WA.