Why wasn't there any mention of traveling distance in the article or map? While it would make sense that the rural areas earn less, and therefor spend a higher

Why wasn't there any mention of traveling distance in the article or map? While it would make sense that the rural areas earn less, and therefor spend a higher percentage on the relatively constant gas prices, shouldn't it also be considered that those in rural areas must drive farther to reach their destinations, and across unimproved roads at times? In the more populated areas, we may only drive 10 - 50 minutes to our destination, and most of that might be in traffic (at least here in southern California). Of course we wouldn't need to spend as much in gas. Everything's closer.