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The Canadian Active Control System is a network of remotely controlled Global Navigation Satellite System (GNSS) monitoring stations dispersed across Canada. Individual stations are referred to as Active Control Points (ACPs). Each ACP is equipped with a high-accuracy, dual-frequency GPS receiver and an atomic clock. These stations monitor the accuracy and availability of GPS reception in their respective locations. Their data is transmitted daily to a facility in Ottawa for further processing and storage.

History
The network was officially established in 1993 through collaboration between various government agencies in Canada, with only 5 active stations. As of 2016, the network has expanded to include 82 monitoring stations with 6 additional stations proposed for construction. Many stations are operated by non-government agencies and are integrated into the network through the collaboration of their operators.

The Canadian Active Control System (CACS) is a network of Global Navigation Satellite System (GNSS) monitoring stations dispersed across Canada. Individual stations are referred to as Active Control Points (ACPs) each of which is equipped with a high-accuracy, dual-frequency GPS receiver and an atomic clock. The stations are operated by Natural Resources Canada in collaboration with various provincial agencies.

Historically, geographic benchmarks(?) consisted of a physical object placed at a location whose coordinates were very well known. Due to tectonic shift(?), locations on the earth's surface

Purpose
Due to plate tectonics, the surface of the earth is constantly moving relative to its lower layers. The speeds at which this happens are generally very small, often measured in millimeters per year. This will cause the geographic coordinates of a seemingly-rigid landmark (such as a building) to slowly change with time. This deviation, while small, can cause accuracy issues in certain application requiring very accurate GPS positioning, such as aviation. As such, a method to track and adjust local GPS coordinates was required by the Canadian government.