Geographic Information Systems (GIS) is a system for the collection, processing, organization, analysis and presentation of spatial data. Geographic information systems include the necessary hardware, software, data and applications. Geographic information systems are used in many fields, including geography, environmental research, archaeology, marketing, cartography, urban planning, criminology (crime maps), logistics, resource management, and health care. With the help of a GIS, for example, civil protection officers can compile information for evacuation plans. Environmental protection agencies can determine which wetlands are located in particularly vulnerable areas. Marketing departments can find out in which areas new customers can be won.
Data Model of Geographic Information Systems (GIS)
Data models describe what data can be stored in an information system and how this data is structured. It is therefore information about real objects (such as people, buildings, rivers). These objects are described by selected attributes. For example, you can assign the attributes district number, building number and type of use to all parcels. The properties mentioned are those that designate an object of the type parcel (federal state, municipal area, parcel, parcel counter and describe its nature. One also speaks of “descriptive data”, “thematic data”, “factual data” or “attribute data”.
The “classical” information systems are limited to the pure management and processing of factual data. In GIS, the so-called geometry data is compared with the factual data. They describe the geographical location, shape, orientation and size of objects (see also spatial objects). A distinction is made between vector data and raster data. Vector data represents object geometry using graphical elements (for example, points, lines, arcs). Raster or pixel data is usually created from digital images (map images or aerial or satellite images).
In the case of vector data, the geometry of a parcel is specified in the form of the boundary point coordinates and the geometry of the boundary lines (distance, arc). The excerpt of a digital aerial photograph (usually in the form of an orthophoto) represents the parcel geometry in the form of raster data.
In addition to the information of the individual objects, information systems also store relationships between these objects. They can be factual relationships or spatial relationships, or both relationship categories can be mapped. A factual relationship can be established.
Data Structure Model
A data structure model specifies how objects and their mutual relationships can be mapped in an information system, especially a GIS. For example, the relation model has prevailed for the storage of object properties and relationships. All attributes of similar objects are managed in tables; The same applies to the relationships between the objects.
Vector-based data structure models make it possible to describe the object geometry using geometric elements (points, arcs, lines); these elements can be combined into higher-value geometries by ordered or unordered grouping (lines or surfaces). Vector data can be linked relatively easily to factual data.
The raster-based data structure model knows only one data structure element, namely the raster element, also called pixels or “pixels” depending on the type of grid. Two properties can be assigned to the grid elements: geometric and radiometric resolution. The geometric resolution indicates the length and width of a grid element in nature; the radiometric resolution refers to the distinguishable grey values per grid element.
With growing amounts of data and the increasing spread of geographic information systems, it is becoming increasingly important to manage geodata efficiently. For this purpose, it is necessary to record metadata and update it continuously. Some GIS offer built-in functionality, while other systems leave it to the user to manage metadata using other software products.
At the beginning of the GIS era, only a few GIS basic systems used marketable database systems for the storage of factual and geometry data (primarily vector data). A variety of systems were based on proprietary database management systems. Today, the use of marketable relational or object-relational database systems for geodata management has become established. Conventional databases cannot efficiently manage geodata. Therefore, for many commercial and open source databases, there are extensions for the management of geodata.