Fundamentals on data visualization. Data visualization has become a modern communication tool for revealing the power of data. With its help, the stories that lie behind numbers can be told in a clear and consistent way. This saves time for presenters and audiences alike, underlines the significant parts of a message, and helps to shape a narrative. An image becomes an integral part of the story. And the more important that part is, the more accurate and relevant the image should be. So, how can this accuracy and relevance be achieved? The Diagrammm project offers the solution to this problem. Diagrammm has been developed as an online source of data visualization grammar. It can be seen as a handbook for designing various types of visualization in ways that are both appropriate and fit-for-purpose. It deals with the basic, fundamental principles of good information graphics.