A

Arc

A topological entity that starts and ends at a node. Although it is often graphically depicted as a line, an arc only denotes a topological link between two nodes, and the geometrical shape of the link is not important. It is also called a link, an edge, or a 1-cell.

Attributes

Characteristics of geographic features. Examples are area, length, owner name, and address.

Attributes, Non-Spatial

Attributes that are not related to the geometry of features. Examples are population of a country and name of a highway.

Attributes, Spatial

Attributes that are directly or indirectly related to the geometry of features. Examples are length of a road and area of a country.

Attributes, System-Defined o

Those attributes which are managed directly by CARIS.

Attributes, User-Defined o

Those attributes which are not managed directly by CARIS but are stored separately in a relational database.

 

B

 

Bounding Rectangle

The smallest upright rectangle enclosing a feature, and it is also called a minimum bounding rectangle. It can be defined by two diagonal points, one from the smallest x and y coordinates, and the other from the largest x and y coordinates of the feature. The main use of this rectangle is to approximate the shape of feature so as to reduce the time it takes to retrieve features.

Buffer Zone

A modeled region around a feature. It is usually described as a polygon with its boundary at a constant distance from the given feature. A buffer zone around a point is a circle.

 

C

 

Co-locating lines

Lines that share the same space. For example, a river and an international boundary co-locates if they share the same line.

Control Points

They are points which can be used to relate and then transform geometric objects from one configuration to another. If the two configurations are in different coordinate systems, control points are used to transform the objects from one system (such as a digitizer coordinate system) to another (such as a ground coordinate system). If the two configurations are in the same coordinate system, control points are used to transform from a distorted configuration to a more accurate one.

Coordinate, Absolute

Coordinate with its value measured from a single origin in the coordinate system. See also Coordinate, Relative.

Coordinate, Relative

Coordinate with its value measured from a nearby point instead of from the single origin in the coordinate system. The purpose is to reduce its magnitude so as to save storage space. See also Coordinate, Absolute.

Coordinate System

It is a means of specifying unique position for geographic features. In a two-dimensional coordinate system, two coordinates are used to specify position on a plane. In a three-dimensional coordinate system, an additional third coordinate is used to specify elevation or depth.

Coordinate System, Geographic

A coordinate system defined over a mathematical body, usually an ellipsoid, approximating the earth. The coordinates are in degrees of latitude and longitude.

Coordinate System, Ground

A coordinate system defined over a flat map. The coordinates are usually in metres along the Northerly and Easterly directions.

Coordinate System, Scaled Ground o

A coordinate system which is a scaled version of the ground system. The constant scale factor applied to the coordinates helps to change them from decimal numbers to integers, thus reducing computer storage.

Corridor

Same as Buffer Zone.