252 Computing in Geographic Information Systems
R-tree: A spatial indexing technique which groups entities according to their
proximity by using minimum bounding rectangles. Hierarchies of rectan-
gles may be established. When querying the database any search is di-
rected to the rectangle and any subsequent lower-level ones which contain
the item of interest.
Run-length codes: A compact method of storing data in raster databases
which simplifies the grid on a row-by-row basis by coding the start and
end values of contiguous cells for each class.
Sampling: The technique of obtaining a series of measurements to obtain a
satisfactory representation of the real world phenomenon being studied.
Scale: The metric property of a map or an image which defines