I often find it useful to look at systems in terms of pressure distributions. I don't know about parking lots, but looking for seating in trains is similar. The

I often find it useful to look at systems in terms of pressure distributions. I don't know about parking lots, but looking for seating in trains is similar. There I visualize people as molecules in a gas. They tend to distribute evenly. However the passages between cars are high-friction so pressure differences show there. As I walk between cars I can gauge the pressure differential and whether it's sensible to continue walking that direction. For the parking lot it would have to be a column of air. As you descend towards the entrance, pressure increases. The rate of the pressure increase forecasts saturation.