This unit includes relevant tessellation data models. Besides features (sometimes also called geo-objects) geo-fields play and important role. In recent literature tessellation models are classified as discretizations of fields. In traditional GI literature tessellations are defined as important data structure itself. Tessellation discretise a continuous surface into a set of non-overlapping polygons that cover the surface without gaps. Tessellation data models represent continuous surfaces with sets of data values that correspond to partitions. Important tessellation models are Grids, TINs and Voronoi diagrams.