Geographic feature

Geoobject referred to in the geography of the earth on a past or present actually existing object that is uniquely referenced by spatial data. It is in the stricter sense of geography is an identifiable part, in the broader sense of geoinformatics an identifiable feature of the earth's surface, as it is relevant for the cartographic representation on general - geographic and hence topographic maps or geographic information systems.

• 3.1 geometry 3.1.1 Grid Model
• 3.1.2 Vector Model

Definition

A geographic object is a localized place on the earth's surface, the tangible or intangible by user definition properties are mapped. This definition takes place in specialized - geo - context.

Following the terminology of the United Nations Group of Experts on Geographical Names ( UNGEGN ), the term specifically places on the earth's surface, while not apply to a topographical object this limitation.

Geoinformatics defines the geoobject as " a custom space -related phenomenon that can be modeled or represented. "

In contrast to general definitions or descriptions ( phenomenology ) of formations of geography, these are certain individual, by their position (geographical coordinates) detectable locations. Collective terms such as mountain, island or bay describe a variety of similar objects. Individual structures of these families of objects ( object classes ), such as the mountain Zugspitze, the island of Corsica or the Bay of Gdańsk are identified by their designation - identified and can be easily recorded cartographically about their unique terrestrial coordinates and thus entered in maps and atlases worldwide - their individual name, a toponym be.

Objects and facts

Geo-objects can be divided into two categories

• Objects in the narrower sense are the concrete, animate and inanimate structures of our environment. These are perceptible and visible in most cases. They can thus be referred to as phenomena or phenomena.
• Facts describe the intrinsic characteristics of an object or its relationship to other objects. In the facts of an object it comes to certain, often not immediately perceptible complex properties. So it can pass an object as an attribute of that object and ground the facts soil climate in an object model. This situation can be described as an independent object class. The spatial reference of facts is represented by the set of those objects to which the facts will be assigned.

Relationships between objects can be illustrated in more detail with a specially created object. In this context, the reference in object-oriented design by an association class.

Dimensional classification

A distinction is made between

• Areal geographical objects,
• Linear geographical objects
• And dot-shaped geographical objects.

An important factor in deciding which object is classified as, is the map scale, the representability and the visibility.

Cartographic presentation

Example: An areal square forest in the natural dimensions of 10 m × 10 m extension has the goods listed below in the following scales card dimensions:

In a sign of accuracy typically 0.1 mm to 0.2 mm is clear that the forest is barely perceptible as the area as early as the scale of 1:10 000. For this reason, in these cases (where the forest has such importance that it should be displayed ) is only a punctiform display possible. The selection of the objects is shown in general or its simplification is called generalization.

Modeling of geo-objects

Geoobjects form elements for modeling the real world in geographic information systems ( GIS). In general, a geoobject four information technology dimensions - also called components - on:

The object can be composed of elementary or complex as desired. Geo-objects are described by geo-information.

Each object represents a unique piece, but is also part of an object class. In the object class the general appearance of an object is defined (eg whether it is point-like, linear or areal through which attributes it is described in detail, what relations are possible or necessary ). Each object must be provided with a unique key or identifier for identification.

For the standardization of geospatial information, the ISO 191xx series of standards was created by the ISO. In this context, the ISO 19109 standard governs the rules for the modeling of geo-objects. It will feature models introduced for this purpose the concept of the General.

The object modeling provides a structure by bringing the individual objects in a context that links them to a certain extent according to the laws of the real world. This ultimately results the digital object model ( DOM).

The modeling process and its documentation are an important phase in the design of a GIS Represents the digital object model has finally decisive influence on the analysis and visualization capabilities of the system.

The modeling in a GIS is done using different techniques: If the model is stored in a relational spatial database, so it is called a data - or structure-based modeling. Objects are mapped in the form of relations. At runtime, the GIS software can calculate an enriched by methods and therefore more powerful virtual object model (on production of a class hierarchy) arise that exists only in memory and is responsible for the actual dynamics in the information system.

Geometry

The geometry describes the spatial position of an object in the 2 - or 3 -dimensional space. It includes all information concerning the absolute spatial location and extent of Geoobjekts based on a spatial reference system. For continua, which are spatially unlimited, there is the geometric information in the location specified for numeric values ​​that continuously change from place to place ( value fields ).

To describe the geometry, two models are widely used:

Grid model

In a grid model of the area of ​​interest is divided into sub-areas with homogeneous semantics. One speaks in this context of mosaic or tessellation. The most common form of tessellation is the division of space in square or rectangular grid cells ( height). The semantics is shown by the numerical values ​​of the matrix elements. This gray value is to be interpreted not as a color but as secondary information. Thus, the gray value of a grid cell is in an infrared receiver for a semantic statement: eg for the vitality factor of the plants.

The grid geometry is well suited to describe facts and scale for the layer concept. So arise, for example in overlapping zones of two planes specific gray values. Through the regular grid it is an easy mathematical exercise to calculate the total area of ​​the overlap region.

The essence georelationaler models can be simulated by pointer in the grid model that point of a grid cell to a property file where detailed semantic information is available. The cell value plays the role of a key for a file or file section in this context. This pointer must not be defined for each grid cell. It satisfies the reference to a centroid ( internal key ), which subsequently the external file referenced -

Typical file formats are: BMP, TIFF, GIF, JFIF

Vector model

Vector models are based on points and lines. Surfaces are represented by closed Polyonzüge. Vector models are also referred to as lineal models, while raster data, a brain area model represent ( in 3-dimensional space wireframe versus volume model).

The vector model is well suited to represent their linear objects (such as lines, roads or river systems).

Vector data require less memory than raster data, although available for these very powerful compression algorithms. The semantics associated with the geometric elements. In contrast to the raster model, in which the gray value of a cell is an implicit assignment, links must be explicitly defined in the vector model. One speaks in this context of a georelationalen model.

The elementary parts to high-order structures ( graph structure) are assembled. Also on this level can be associated with thematic attributes.

In vector models are cross-sectional and area calculations more complicated than in the grid model.

Typical file formats: WMF, shapefile

Topology

The Topology deals with those properties of the spatial reference, which are independent of the metric. It characterizes the spatial relationships to each other of geo-objects and is therefore also referred to as " geometry of the relative position ": environment, containment, neighborhood or intersection are characteristics of topological relations.

Every metric space is simultaneously also a topological space. The unchanged in geometric rotation, translation or scaling topological properties is called a topological invariants.

Topological elementary structures are 0- cell ( node ), 1- cell ( edge ) and 2- cell ( mesh ). In the grid model, the topology is implicitly defined by the cell matrix. In the vector model, they must be explicitly formulated. Often topological relations can be derived from calculations although the geometric model, however, forms an efficient topological modeling an important basis for data consistency.

Semantics

The semantics is a supplement to the geometry. While the geometry after the "where" asks the question of semantics according to the " what " refers.

The semantics describes - in contrast to the outward spatial reference - all inside, related to the nature of the object information. Semantics is the meaning of a Geoobjekts in subject-specific context. This meaning arises in spatial object models by belonging to a particular object class. Refined it is through the interplay of class- related non- spatial attributes. These may be qualitative or quantitative in nature. Quality refers to information on the nature or structure of an object. Quantity, however, focuses on quantity, value, intensity or size.

The semantics results from the structuring of trade data and the observation as a whole. A special feature of the semantics is that it is by no means free from subjectivity. The user associated with an object has certain characteristics which are determined by his living conditions or its specific way of looking at the object.

However, you can exclude the semantics in terms of individual perception and use the term representative of the importance that is given to an object with respect to a specific issue by qualified attributes.

Dynamics

With the concept of dynamic all temporal changes of geo-objects are characterized. The intensity of dynamic modeling depends on whether the objective of the system a "snapshot " is used (static) or a dynamic behavior is paramount.

Modeling to issues such as flow, transport, regional development, etc. pay attention to temporal changes. Considerations for introduction and visualization of dynamic play in these cases, of course, a very crucial role.

Examples of geo-objects

Model of a river route:

• Geometry: Description of the stretch of water by a line.
• Topology: The river segment ends at the mouth of the river into the Danube.
• Semantics: measurement and observation values ​​for water level, number of plant species, etc.
• Dynamics: changes in geometry and some features of the semantics by erosion of the watercourse.

Model of a climate control system for measuring meteorological parameters:

• Geometry: describing the spatial location of the climate station by geographic coordinates.
• Topology: The Air Station is located in the community of Great Gerungs.
• Semantics: measured data for air temperature, precipitation, air pressure, etc.
• Dynamics: Temporal variations of the meteorological parameters.

Model of a biotope:

• Geometry: Outline of the biotope with a closed polyline (polygon ).
• Topology: The biotope is intersected by a road.
• Semantics: biodiversity, biochemical cycles, the predominant soil type, etc.
• Dynamic: topology change by abandoning the road and restoration of the former traffic areas.