This chapter presents an overview of some of the concepts behind spatial data as well as practical ideas about collecting data and incorporating it into one's maps. The most basic distinction in data used in mapping is between spatial and aspatial data. Spatial data can assume a variety of forms, but two key file systems continue to dominate the scene. Digitizing is now performed on computer screens with digital images. A good example of useful data in the form of static, ungeoreferenced maps is the Sanborn insurance maps. Ministries or departments of governments often publish a wealth of data that empower users to perform mapping work. A critical distinction often made in scientific and mapping endeavors is between primary data and secondary data. A problem facing modern geospatial data is data error propagation. The perception of maps as authoritative sources of data means that even basic and seemingly trivial decisions about symbolization can end up having meaningful real-world implications.