The second issue concerns what is to be visualized. According to Card, information chunks to be visualized are different at each level so that different visualization techniques should be used. Objects to be visualized include a variety of datasets from one single object to whole datasets and even the relationships among the objects. If visualization intends to be used for comparing, combining, or grouping multiple objects and eventually providing information seekers with more value-added information, visualization must convert the appropriate data to relevant information. As the potential users of visualized information systems have various levels of experience, the actual design of visualized information systems must be preceded by user studies and usability testing should be considered in the post-design stage.
Different users have different searching styles and preferences.
Thus it is important to provide appropriate techniques for satisfying a user' s information needs in specific circumstances. Task analysis is another critical issue for visualization which needs to be applied successfully in these systems. One particular factor which should affect the organization and presentation of the objects is the task being undertaken by the user. Visualization in information systems has neglected the study of task analysis. Visualization in information systems should be designed to allow users to monitor the system from their perspective and manipulate it for their needs.