Presents an microworld for investigating the effects of visualizing expanding search areas to support the building of a naval force's common operational picture. The microworld simulates naval warfare operations, and in it, two participants can play against each other in an operations area where both own units and neutrals may be present. The participants control combat vessels used to locate and attack the enemy, and high value objects that should be protected. The map of the operations area is configurable and the units' weapons and sensors can be defined by the experimenter. The microworld displays an individual operational picture to each player complied from the sensor information provided by that player's units. To investigate visualization, expanding search areas can be added to enhance the operational picture, and algorithms based on these areas can be used to let the computer help the participant identify enemies from neutrals. The integration of expanding search areas into the operational picture is illustrated. The unit classification algorithms based on expanding search areas are explained, and examples of how they work are presented. Experimental setups are presented together with initial evaluations of the microworld.