A sonar imaging system includes a sonar transducer mounted to a motorized steering unit configured to rotate the sonar transducer about a vertical axis. At least one processing element receives sonar return data from the sonar transducer and controls rotation of the motorized steering unit in response to user input. The at least one processing element determines, for received sonar return data, corresponding heading information and geographic position information associated with the sonar return data and associates the sonar return data with the heading information and geographic position information. Sonar return data collected during rotation of the sonar transducer through an angular range may be used to generate an accumulated image. Accumulated images may be displayed in a two-dimensional or three-dimensional view such that the underlying sonar return data is rendered at geographically correct positions and maintained in geographic alignment as a marine vessel moves.