Q
quad, quadrangle, map quad or map quadrangle
The geographic area covered by a map. One kind of map quadrangle is the 7.5' x 7.5' area that is covered by a standard USGS 7.5' topographic map. Referring to a 7.5' map quadrangle does not imply the presence of an actual paper map. The term may simply designate the area covered by electronically stored materials.
Quad tree
A spatial index which recursively decompose a data set (eg image) into square cells of different sizes until each cell has a homogeneous value. Quadtrees are often used for storing raster data.
quantization
Dividing a continuous range into a finite set of discrete values called quantization levels. If too few quantization levels are used, false contours may appear in an image. Quantization levels are often referred to as "gray levels," but the concept can also apply to color images.
query
A query, or database query, is a set of instructions defining attribute criteria that are used to select records from a database. The Specific spatial elements (such as lines or polygons) to which those records are attached are then automatically selected for the current process.