Earth mover's distance (EMD) Distance function that takes into account both   Feature value   Feature location Useful for images, trees, music, shapes, etc. Considers each feature value as "mass" in that spatial location EMD tries to find out minimum "work" done in transforming object to object   Moving 1 unit of mass through 1 unit of distance is equivalent to performing 1 unit of work Concept of ground distance from each feature location of object to each feature location of object   Matrix of size   m and n are number of features (or regions from where features are calculated from) in object and object respectively