Another way to take into account the non-spatial attributes of objects is as a kind of “weight”
when calculating the “cardinality” of the neighborhood of an object. To keep things as simple as
possible, we will not introduce a weight function operating on objects, but a weighted cardinality
function wCard for sets of objects. The “weight” of a single object o can then be expressed by the
weighted cardinality of the singleton containing o, i.e. wCard({o}).