A Control network or simply Control, is a set of reference-points of known geospatial coordinates. The higher-order (high precision, usually millimetre-to-decimetre on a scale of continents) Control points are normally defined in both space and time using global or space techniques, and are used for "lower-order" points to be tied into. The lower-order Control points are normally used for engineering, construction and navigation. The scientific discipline that deals with the establishing of coordinates on points in a high-order Control network is called geodesy, and the technical discipline that does the same for points in a low-order Control network is called surveying. Classically, a Control is divided into horizontal (X-Y) and vertical (Z) Controls (components of the Control), however with the advent of satellite navigation systems, GPS in particular, this division is becoming obsolete.
