Question

what a spatial model is by using some examples of real-world entities and how they could be modeled in GIS (e.g. the city of Denver could be modeled as a vector point in a map of the US or as a vector polygon area in a map of Colorado). What are the limitations of the spatial data models with regard to your example?

Answer 1

The database community used to stipulate that a database stores representations of those concrete and abstract things in the real world the applications are interested in. These representations are organized (structured and formatted) so that the data that is required by the applications can be stored in the database and later retrieved without ambiguity. Assume, for instance, a city management database is designed to support a variety of applications. The database stores data on roads within the city limits. A traffic management application considers roads as connections between two points. Its requirements may be translated by defining in the database schema a RoadSection object type to represent, for instance, each road segment between two consecutive crossings. The RoadSection object type may be given properties, e.g., whether the road section permits movement only one-way or both ways, the number of lanes each way, and the average traffic density in each direction. Each instance of the object type is a (database) representation of a piece of reality that can be distinctively perceived when looking at the real world (e.g., the stretch of Broadway between the 42nd and 43rd streets). In this paper we adopt the database terminology, which refers to the description of data in a database as the database schema, and to the set of modeling concepts (object type, attribute, etc,) as the data model. In GIS applications the database schema is often referred to as the database model, and the data model is called the meta-model.