M: Geodata management and modeling

Geodata management comprises both the aspects of data modeling already addressed above and the concrete implementation of data structures in the database as well as the provision of methods for manipulating this data (creating, inserting, deleting, changing data records, etc.). The information available in the maps, card indexes and other collections must be described in the application context and stored in a structured form. Each geoobject is described in GIS by its components. Accordingly, the GIS must be able to model the real world geometrically, topologically, thematically and temporally, to enrich it with metadata and to manage it in databases. A comprehensive overview can be found in Bill, 2016, Chapter 6.

For the administration of vector data today's GIS mainly use (object-)relational databases, which are extended by functions for handling geometries. These databases then support the storage of the coordinates of point, line and polygon geometries as well as the calculation of spatial indices for quick access to the geometries. From the user's point of view, the geometries then present themselves as a further attribute field alongside thematic, and temporal attributes in the tables for managing the geoobjects. Furthermore, special tables can be created to manage the topological relationships within and between the geoobjects.

From the point of view of information technology, the administration of spatial data represents a non-standard application of database management systems (DBMS). Standard applications of DBMS are to be seen in reservation and banking system, in the material order and production process, whereas the areas of the CAD, the geo-information systems and the printed circuit board design are considered as non-standard applications (Bill, 2016, S. 435 ff.). Database systems that adequately support the storage of geodata and geoobjects as well as the processing of spatial queries are called geo or spatial database systems.

Geodatabase system

According to Brinkhoff (2013), a geodatabase system must possess a number of capabilities that are generally available today in object-relational databases with spatial extensions (cf. Bill, 2016, p. 444 ff.):

  • The geodatabase system must offer geometric and topological data types that can appropriately represent geometric and topological data. For example, data types are required for points (nodes), polylines (edges), polygons with holes and sets of polygons (meshes) in 2D and solids in 3D.
  • A geodatabase system must provide methods for these geometric and topological data types that allow the execution of geometric and topological functions. Such functions calculate, for example, the intersection between two surfaces, determine the length of a line, or check the containment within surfaces. They can be used by the user in the query language of the database system. This can be done either in the query condition to determine the data from a particular area, or with respect to the data sets that meet a non-geometric query condition, for example to calculate its area.
  • If a query condition contains one or more operations that have a spatial reference, the query is traced back to one or a sequence of spatial basic queries. Examples are the point query, which determines all objects whose geometry contains a query point, or the rectangle query (clipping), which determines all geoobjects intersecting the rectangle for a given query rectangle. The processing of spatial basic queries and other geometric operations must be sufficiently efficient. This requires suitable algorithms and data structures. This requirement includes, for example, that geoobjects are managed by the database management system using spatial indices, and that efficient algorithms for solving geometric search queries are implemented.
  • The geometric and topological data types and functions must be specified in such a way that they can be easily used by applications outside the geodatabase system in the sense of an open GIS. In order to achieve interoperability between different applications, the data models must comply with generally accepted standards. This enables the integration of spatial data into the traditional IT infrastructure of an organization and its business processes.