When latitude is measured, the starting point is the equator (0 degrees latitude). To give you some perspective, the North Pole is 90 degrees north, and the South Pole is 90 degrees south latitude. Portland, Oregon, is at 45.5 degrees north latitude, and Alice Springs, Australia, is at 23.7 degrees south latitude. The closer a location is to the equator, the warmer the climate tends to be.
Alice Springs, in the southern hemisphere, is much closer to the equator than Portland in the northern. This shows in the average temperatures in the two locations. Because of its latitude, Alice Springs can get up to 113 degrees Fahrenheit in the summer. Because of its latitude, Portland's average summer temperature is less, at 81 degrees.
Other factors affect the climate of the two areas as well. Alice Springs is an interior, desert-type area, which allows for low night-time temperatures. Portland is a coastal area, near the Pacific Ocean. The Pacific current brings cold ocean water down from the north, and the area receives a good amount of rainfall.