Humans have remarkable perceptual capabilities. These capabilities are heavily underestimated in current visualizations [759]. Often, this is due to the lack of an in-depth user study to set the requirements for optimal visualizations. The designer does not understand what kind of information should be visualized, how it should be presented or what kind of interactions should be supported. The key elements of successful information visualization are the correct data using the best visualization technique and the best interaction techniques with respect to users. If one of these elements is ignored, people might interpret the data in the wrong way and thus might not understand the underlying information or a pattern.In order to design effective interactive visualizations, it is important to take into account the limitations of human perception, context of use, and the goals and activities that are to be performed to reach these goals. In order to obtain a usable application, developers have to pay attention to the user's working environment and tasks; this focus-on-user idea is comprised in the human-centered concept.The next section discusses usability (the property of being usable) from the human-centered point of view. Usability has application in many areas, but our focus is on the human-centered approach to design of interactive systems, also called user-centered, in order to inform the reader on how to design visualizations according to human cognitive and perceptual abilities, specific to the context of use and goals of potential users. Then, the usability concept is explained in the "Usability in Human-Centered Design" section. The next Section "User Aims and Requirements" discusses how to define a user group, establish user goals and requirements. Finally, an overview of the different evaluation methods and current evaluation practices, including the practical issues of experiment design that can help to improve the effectiveness of visualizations is presented in the "Evaluation of Visualizations Environments" and "User Studies and a Science of Visualization" sections.
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