title: Manhattan distance generalization
body: <p>For a research I'm working on I'm trying to find a satisfying heuristic that is based on Manhattan distance which can work with any problem and domain as an input. Which is also known as domain-independent heuristic. 
  For now, I know how to apply Manhattan distance on a grid based problems.
  Can someone give a tip how to generalize it to work on every domain and problem and not just grid based problems?</p>