There are different types or levels of control networks depending on where and why they are established. A control network may have very accurate positions but no elevations (called a Horizontal Control Network) or very accurate elevations but no positions (called a Vertical Control Network). Some points in a control networks have both accurate positions and elevations. Control networks range from small, simple and inexpensive to large and complex and, yes, you guessed correctly, very expensive to establish.

A simple, or local, control network covers a small area (the size of a subdivision or open pit mine). It may use a "local" coordinate system that will allow you to position the features in relation to the control network but doesn't tell you where the features are on the surface of the earth.

An advanced control network, which typically consists of a few well-placed horizontal and vertical control points, is established by very precise measurements, using the best equipment and methods available and forms what is called the primary control. Additional control stations located across the project area may be added using less precise measurements to form the secondary or supplemental control. This type of control, while less accurate, is more easily found, less expensive to establish, and more convenient to use.