Figure 9: Minimum Manhattan distance problem in two examples.
From: Multiple tipping points and optimal repairing in interacting networks
(a) Finding the minimum Manhattan distance between point S1 in the red sector and the green region where the system is fully functional. Equidistant curves are plotted in grey and form a ‘diamond’ shape. The largest ‘diamond’, barely touching the green region and having its centre at point S1, suggests there are two equally optimal solutions to the minimization problem: points R1 and R2. (b) The same geometrical construction for point S6 in the light blue region, suggests a unique solution: decreasing 
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