This chapter covers data visualization and uncertainty, highlighting examples of effective and poor visualization practices. The first part explains key visualization objectives, including exploration, synthesis, presentation, and analysis. Different visualization types are described, such as graphical, visual encoding, and hybrid methods. A detailed focus is given to visualizing uncertainty, ranging from 1 to 3D representations. Strategies for effectively representing uncertainty are outlined, along with practical examples to enhance understanding of data visualization and its complexities. This part concludes with a discussion on human perception, cognitive biases, and heuristic biases in data visualization. The second part includes a practical exercise creating a fan chart to visualize population projections and their uncertainty, using total population data (combined for both sexes) provided by the Population Division of the United Nations Department of Economic and Social Affairs.