The purpose of data or information visualization is to create visual representations of data sets to help to carry out tasks more effectively. This contribution gives a basic overview of this topic. It includes the reference model of information visualization according to Card et al., the different features and classifications of visualizations, as well as practical examples and tools that illustrate the potentials and challenges of the domain. One of these examples is the visualization project "Poppy Field" by Valentina D'Efilippo. Finally, the topic is put into the context of repositories.