[uncertainty] In GIS, a state of uncertainty in data classification that exists when an attribute applies to an indeterminate quality of an object or describes an indefinite quantity. For example, the classification of an area of land as the range of golden-winged warblers (a rare species of bird) is vague for two reasons. The area populated by the birds is indefinite: it is changing constantly and can never be precisely defined. The term “range” is also somewhat vague since the birds migrate and occupy the territory for only part of the year.