For example, let us say we were conducting a study of facial features and we were comparing hair color, nose type and eye shape. Those three characteristics would identify something or someone. What would a good term be for the items that are used to identify a unique point in the problem space?
I looked at a few similar words in the Thesaurus on thefreedictionary.com. For example, under coordinate (n) it yielded co-ordinate, Cartesian coordinate, polar coordinate and number. Most of those were not even synonyms except in the most trivial sense.
"Characteristics" is a superset of what I am referring to, as it includes all characteristics, not simply the ones considered unique or defining.