In this chapter, several characteristics are proposed that help us identify and describe the scope of mobile data visualization, which stretches beyond an intuitive understanding of the term. The focus lies on those characteristics that, particularly in their extremes, differentiate mobile data visualization from other forms of data visualization. These characteristics give rise to dimensions of a design space for mobile data visualization, against which instances may be classified and positioned. The chapter discusses a number of examples to illustrate how the design space makes it possible to describe and compare mobile visualizations.