Recently, in local Wal-Mart parking lot, a young lady I met was insistent that John McCain was her Senator because she was in his district.
Remember, each state has 2 Senators guaranteed to by the Article 1 in the U.S. Constitution. This is regardless of each state's population.
However, the number of Representatives a state may have IS correlated to its population. Arizona has 9 Congressional districts that were last defined based upon input from census data collected in 2010, and thus we have 9 Representatives who each represent Congressional Districts 1-9 The current layout of Arizona's Congressional districts has been in place since the 2012 redistricting effort. You can view the geographical layout of all nine districts here: Arizona's Congressional Districts. You'll notice large variations in the size of the area of each district. The intent is to ensure "X" number of people per Representative, more precisely, the State of Arizona did its best to align approximately 710,000 people per Congressional Representative. So for our state, you can assume that the smaller districts 5 through 9 are more densely populated than are districts 1 through 4.
This is a map of Arizona's 8th Congressional District: Click here