The graph below is a stylized friendly neighborhood. Lines are roads and dots are intersections.
To best protect this friendly neighborhood from enemy attack (e.g., zombies), the goal is to place 4 strike teams (select 4 dots) to minimize the average distance between the strike teams and all other points. Green dots are safe and red dots are in danger. Make as many dots as green as possible.
The score below is the average distance between your operators and the other intersections. The lower the score, the better.