Geographic information visualization provides powerful tools to represent visually the dynamic feature. In order to meet the needs of map symbol design based on modern technology, this paper extends Bertin's visual symbol system to time area. Four dynamic visual variables which are duration, change rate, change order and rhythm have been added to Bertin symbol system. Some of application of variables is discussed, including enhancing spatial location, describing static attribute and describing dynamic process. After assessing the geographic information characteristics in spatial-temporal change, the paper presents the concept of dynamic map. The definition and generalization of dynamic map are illustrated. As to the function of dynamic map, the paper puts forward three implementation areas: post-processing, real-time tracking and movement simulation.