Can You Figure Out This Parking Lot's Numbering System?

Can you explain the numbering system in this parking lot? Like most good riddles, there are several clues hiding in plain sight, and the answer, once you see it, is clear as day. (And, if you're like me, you'll wonder why it didn't dawn on you sooner.)

I'll do my best to moderate discussions below to keep the answer hidden, but definitely avoid the "All Replies" tab below, unless you want the solution spoiled!

Via Boing Boing | H/t io9 reader N. Gordon!