Control area is a coherent part of the UCTE Interconnected System (usually concurrent with the territory of a company, a country or a geographical area, and physically demarcated by the position of points for measurement of the interchanged power and energy to the remaining interconnected network), operated by a single transmission system operator (TSO), with physical loads and controllable generation units connected within the control area. A control area may be a coherent part of a control block that has its own subordinate control in the hierarchy of secondary control.