Time when a fact is true in the abstracted reality.

Process of assessing, by independent means, the quality of the data products derived from the system outputs.

[GIS processing] Variable distance buffer uses a feature attribute from the input to create a ring around the feature that varies in distance.

Quantity having direction as well as magnitude.

[data structure] A vector data model is a common GIS feature representation of spatial information based on defining coordinates and attribute information. Vectors are points, polylines and polygons.

A vector object is made up of three different types of elements that can have associated attributes 1) points, which are single sets of coordinates that define a point feature (such as a well); 2) lines, which are curvilinear strings of coordinates that define a curved line (such as a stream); and 3) polygons, which are collections of lines that inscribe an area (such as a lake), and a fourth type of element, nodes, which are necessary to maintain vector topology.

A data structure for representing point and line data by means of 2- or 3-dimensional geometric (Cartesian x,y or x,y,z) coordinates with exacting topological requirements. In connection with GIS and computer graphics, "vector" can refer to a set of line segments joined end-to-end to make a curved path in space. Vector objects also have a set of attributes (such as ID number, color, drawing style) attached to them.

Vegetation data describe a collection of plants or plant communities with distinguishable characteristics that occupy an area of interest. Existing vegetation covers or is visible at or above the land or water surface and does not include abiotic factors that tend to describe potential vegetation. 

Source: OMB Circular A–16: Appendix E (2002)

Traveller.

Object subject to being navigated or tracked.

Type of vehicle, based on the nature of its construction or intended purpose.

Provision of objective evidence that a given item fulfils specified requirements.

Test developed to prove rigorously whether an IUT is correct.

[data structure] A vertex is a point that specifies a position on a line. Arcs and polylines are comprised of sets of vertices all interconnected in individual features.