Geography Reference
In-Depth Information
terms of relationship vectors. This simple operation is a very powerful trans-
formation. In all cases, obviously the accuracy and quality of a buffer de-
pend on the underlying model and explicit (or implicit) assumptions.
OVERLAY TRANSFORMATIONS
GIS overlay is, depending on who you speak with, the first or second most
important operation for GIS. Either way, it is without doubt one of the most
significant operations. It is also one of the primary transformations, but the
transformations performed by an overlay depend on the type of GI represen-
tation.
Positional GI combines the geometries (points, lines, or areas) of two
data sets based on a common coordinate system. The geometrical transfor-
mation is only the geometric process of determining the intersections
between objects from each data set and the assembly of new objects that cor-
respond to the original objects. Attributes from the original objects are
assigned to the new objects based on the location of the original objects. The
Overlay transforms by combining two
(or more) data sets based on the location of features
in a coordinate system.
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