PPM (pixels per minute). It’s a stat that’s independent of the developer methods but can also be used to complement them.
But that is still very dependent on how long a gamer is expected to remain in certain areas, which depends on the gamer type. Even if you look at a Multiplayer Map, a single level could have many different values because of how the map plays which depends on the game mode; TeamDeathMatch plays vastly different than King of the Hill or Capture The Flag. Each Map+GameMode combination will also have different sections if the team is going for power weapons or support positions. A single map could easily have small zones (indoor corridors), large far zones (outdoor sniping), and medium zones (transition hot-points or choke points).
Talk about High Complexity with High Effort required with perhaps little to no appreciation for the net result.