The widespread propagation of networked computers in Earth and space science and especially the representation of scientific data in formats that can be shared, analyzed and visualized has given rise to exciting new opportunities for exploration and discovery. Data are the representation of some facts. We can see data of various subjects, types and dimensions, such as a geologic map of New York State, records of sulfur dioxide concentration in the plume of Turrialba Volcano, Costa Rica, and the global mean sea level time series derived from radar altimeter records of the TOPEX and Jason satellite series. A unique feature of most data in Earth and space science is that they are georeferenced, which means they contain positional values below, on, and/or above the surface of the Earth. Information is the meaning of data as interpreted by human beings, such as, a geologist may discover some initial clues for shale gas exploration by using a geologic map, a volcanologist may detect a few abnormal sulfur dioxide concentration values in the plume of a volcano, and a climatologist may find that the global mean sea level has been rising in the past twenty years. People use their knowledge to discover information from data. The knowledge is their expertise or familiarity with one or more subjects under working. The discovery process of data to information in turn may make new contribution to people's knowledge.

People not only possess knowledge implicitly in their brains, they also encode some of their knowledge in models, algorithms and programs that can be operated or run by computers and can be reused by other people. Data visualization plays an increasingly important role in the interactions between human and computer, and the Semantic Web provides a broader space for people to share both data and knowledge. This chapter will introduce research topics and applications associated with data visualization in the Semantic Web, with a focus on subjects in the Earth and space science. The text is organized as two parts: the first part is about concepts and theories and the second is about technologies and applications.