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Coordinates and Coordinate Systems
Introduction
Coordinates are unique identifiers which locate points of interest in space with respect to a reference frame. The point of interest may be a survey instrument station or a point of detail such as a land parcel corner on a map or a building feature in a CAD model. Once a point has coordinates associated with it, the location can always be recovered with respect to the reference frame.
The reference frame, also known as the coordinate system, may be a simple rectilinear system or a more complex non-linear system such as latitude and longitude on the surface of the Earth. Coordinate systems may be two dimensional, describing only the position of a point in a plane, like the location of grid intersections on a piece of graph paper. Alternatively, the reference frame may be three dimensional, defining the location of a point in terms of 2D position and height, such as an engineering CAD model of a bridge design.
The final products of plane surveying activities are generally maps or CAD models of the natural and built environment. Coordinate systems are a fundamental part in the creation of these final products as coordinates are used to describe the relationships between survey measurements and interest point locations.