in section 2.1, the two basic data models (vecter and raster models) that are used in ilwis are treated together with the different types of objects (i.e. data objects, service objects, container objects and special objects). in section 2.2 the various types of maps are show point, segment, polygon and raster maps. vector and raster maps can be displayed simultaneously in a map window. in this section and in section 2.3 you will also have a closer look at one of the key concepts of ilwis: the use of domain. a domain lists e.g. the possible unit in a map (as class name or id) or the range of possible value in a map. a representation, treated in detail in section 2.4, contain the information that determine how your spatial data should be represented on screen or in a printout. a coordinate system (section 2.5) contain information on the kind of coordinate you are using in your map.