The creation of a digital representation of the Earth and its associated data is a complex and difficult task. The incredible size of geospatial data and differences between data sets pose challenges related to big data, data creation, and data integration. Advances in globe representation and visualization have made use of Discrete Global Grid Systems (DGGSs) that discretize the globe into a set of cells to which data are assigned. DGGSs are well studied and important in GIS, OGC, and Digital Earth communities. However, DGGSs have not been introduced very well to computer graphics community. In addition, there are many advanced techniques related to geospatial data creation and representation that might be very useful to Digital Earth community. In this paper, we provide an overview of DGGSs and their use in digitally representing the Earth as well as the list of current Digital Earths and their method of Earth representation. In addition, we present key research areas and related papers in computer graphics that are useful for a Digital Earth framework. Moreover, we list a number of applications of Digital Earths and their related works.