An image of Southampton's Dock Head captured from the deck of a Red Funnel car ferry in September 2018. The blue building houses Southampton's Vessel Tracking system (VTS) and organisation that has responsibility for the control of all vessel movements of or over 20 metres in length. The VTS area of control extends over nearly all of the Solent. Dock head defines the demarcation line between the navigable waters of the River Test (left of VTS) and Southampton Water (right of VTS).