In naval terminology a Plot is a graphic display that shows all collated data from a ship's on-board sensors i.e. radar, sonar and EW systems. They also displayed information from external sources ie other vessel or aircraft reports. There are four different types of plot, each with varying capabilities i.e. range, depending on their role;

Air Plot: Used for tracking air contacts i.e. planes and EW information

Surface Plot: Used for tracking contacts on the surface of the water i.e. other ships. It can also perform a variety of roles such as;

• Providing a trace of a ship's own course and speed over time

• Plotting the position of a man overboard
  Man overboard
  Man overboard is a situation in which a person has fallen from a boat or ship into the water and is in need of rescue. Whoever sees the person's fall should shout "man overboard" to alert other crew members and attempt to maintain visual contact with the person in the water...
  
  

• Can be used in naval gunfire support
  Naval gunfire support
  Naval gunfire support is the use of naval artillery to provide fire support for amphibious assault and other troops operating within their range. NGFS is one of a number of disciplines encompassed by the term Naval Fires...
  
   missions to plot unidentified contacts and keep track of friendly forces

• It also plays an important part in anti-submarine warfare
  Anti-submarine warfare
  Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....
  
   operations and using Torpedo
  Torpedo
  The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...
  
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Sub-Surface Plot: Used for tracking contacts below the surface of the water i.e. submarines

General Operations Plot: Used for tracking shipping on a large scale chart. Was also used to display exercise boundaries, airlanes and other significant features of maritime interest. In the R.A.N. the scale used was generally 5 miles to 1 inch OR 10 miles to 1 inch.