GIS Term Glossary
- Attribute
Attributes signify a distinct Thematic Contents of Spatial Objects (-> Geo-Objects) and characterise an -> Entity, an Entity Type, a Relation or a Relation Type in a -> Data Model.
- Attributive Data
Attributive Data represent the Thematic Contents of a Spatial Object and therefore are the Class of the non-geometric Data. Hereby different Thematic Assignments can be described. Other expressions for Attributive Data are the Terms -> Attribute, Thematic Data or also Alphanumeric Data.
- Buffer
A Buffer is a basic -> GIS-Analysis Function. An Buffer is a Zone in a distinct Distance from a physical Entity, like a Point, a Line or a Polygon, which was defined be the user. The creation of Buffers to determine the Proximity of certain Entities is an often used application of the GIS-Analysis.
- CAD - Computer Aided Design
Using CAD one can construct and design by a Computer Program. Using CAD Programs not only Technical Drawings can be generated. These Programs also allow the Construction of three-dimensional Volume Models. Two- or three-dimensional Drawings and even animated Visualizations of the Objects can be derived from these Models. Some CAD Systems also contain Functionalities of GIS Products.
- Consistence
Completeness and Absence of Contradictions of the Computer-internal Representation of real-world Objects. Geometric and semantic Consistence of the Data. Redundant Data Representation can lead to Inconsistence. But Data Consistence is one of the most important requirements of an Information System. A so called Database Management System (DBMS) ensures Consistence, if its Service Functions bring a consistant state of its Databasis into an other consistant state. Also Topological Conditions are Consistence Conditions which are needed for a-> GIS.
- Coordinate System
A Coordinate System is a System consisting of two/three (generally n) Coordinate Axis and/or Directions in an Area/in a three- (generally n-) dimensional Space, in which Coordinates can be assigned to geometric Entities (e.g. Points, Lines, Areas) - and vice-versa. A Coordinate System is a mathematical-geometrical system of arrangement, which enables the user to georeference -> Geodata (-> Georeference).
- Database
A Database is a Collection of joined Data (i.e. having a Relations to each other), which are stored in a computer-based Information System to support one or more Applications, and which is independent of the Computer Programs using it. The Database is the central Component of a modern Geo-Information System.
- Dataformat
A Dataformat is a Specification which defines, how Data are structured in a File, and which distinguishes special aspects like the Sequence of Data Items, their Length and important Header Data. To ease the Data Exchange there are some standardized Exchange Formats. Many Formats are saved in form of user-readable Texts (ASCII) as Tables and also with a simple Syntax. Important examples are -> DXF, -> Shape File and -> GML.
- Datamodel
A Datamodel is an artificially created, abstract Image of a Part of the Reality, with the aim to be able to map distinct circumstances, e.g. the Informations needed for a business process in a enterprise, into certain Data Structures.
- Data Schema
A Data Schema contains the Description and Definition of -> Object Classes, which are Representations of real world phenomenons.
- Dataset
A Dataset is a Set of independent Data Fields, which describe a Unity, which is also grouped as a Unity for Processing. A Dataset consists of Data Fields.
- Datum, geodetic
A Geodetic Datum is a geodetic Surface of Reference (e.g. Sphere, Ellipsoide), which is defined by five Parameters: Longitude and Latitude of a Central Point, Azimuth of a Line beginning at this Point and two Constants describing the Form and Scaling of the Referenc Surface. Important Geodetic Datums are NAD 27 (Northamerican Datum of 1927), ED 50 (European Datum of 1950), WGS84 (World Geodetic System of 1984) and the Potsdam Datum (Germany).
- DEM - Digital Elevation Model
A DEM is a digital Representation of the Terrain Surface by spatial Coordinate Triples of a Set of Surface Points, e.g. in form of Triangle Networks or Grids. A DEM is also a Dataset used by the Survey Administration. From a DEM e.g. Maps with Height Contour Lines can be derived; also Volumina and Inclinations can be computed.
- DOM - Document Object Model
The DOM is a W3C Specification, which allows Computer Programs to access a Data Document by a general Procedure in form of a Set of Objects. Like Object-oriented Programming the DOM consists of a Set of Classes containing Methods and Attributes. It is an essential Application Programming Interface (API) for the access of HTML- or -> XML-Documents, e.g. -> GML Files.
- DXF - Data Exchange Format
DXF is a -> CAD Exchange Standard definded by the Autodesk company for its Product "AutoCAD", which developped also - in the -> GIS Science - to a Quasi-Exchange-Standard for -> Vector Data.
- Entity
An Entity is an individual, distinct copy of Elements in the real world or a world of imagination. Entities are combined in Entity Classes. Entities emerge by Abstraction and can be represented in a -> Database.
- EPSG - European Petroleum Survey Group
Since 2005: OGP Surveying & Positioning Committee. The EPSG administers a List of -> Coordinate Systems, which is used by the OGC-Specifications and by OGC conforme Web Services. By the EPSG-Code in -> GML the geodetic-> Reference System and the -> Projection of the Coordinates are determined.
- Export (Interface)
Write Process of an Application to process Data (Files) to be read by another Application (-> Import). This kind of Software is called an Interface.
- Fiducial Point
Fiducial Point, Reference Point or also -> Fixed Points are Points, by which Data in different -> Coordinate Systems can be transformed into one common Coordinate System. Fiducial Point is a term in the Field of Photogrammetry to determine the absolute Orientation, or when digitizing for -> Transformation from Digitizer Coordinates to real world Coordinates.
- Fixed Point
A Fixed Point is Point in the Field of Surveying, which is determined in 2D and/or Height. It is part of the Trigonometric Field or the Height Field, and defines the -> Reference System of a Country or of the Earth.
- Geodata
Geodata are Data describing Objects, Topographic Forms and Infrastructures on the Earth, whereby as essential Element a -> Spatial Relation is necessary. They describe the Objects in the real world. Geodata can be connected by a Spatial Relation, from which new Information can be derived using -> GIS-Functionalities .
- Geocoding
Part of determining a -> Georeference. Means the effective Transformation step which is necessary to convert Data, having different Georeference, into another -> Reference System. Using -> Raster Data this encludes e.g. the Resampling of the Picture Elements (Pixels). When Coding Addresses the Relation between the geometric-topological Relations of the Street Network and the Areas of Streets/House Numbers have to be considerated.
- Geo-Object
A Geo-Object is the most elementar Entity, which is contained in a -> GIS, as it is seen by the user. It can be the image of a concrete physically, geometrically or semantically described Entity of the Earth and has a unique Identity.
- Georeference
The Georeference is a Property of a spatial Dataset, which determines the geodetic -> Datum and the (Mapping-) -> Projection of the Dataset, i.e. the geodetic -> Reference System on which it is based.
- GIS - Geo Information System
A GIS is a computer-aided System, which consists of Hardware, Software, Data and Applications. Using it spatial Data can be registered and edited, saved and reorganized, modelled and analysed, as well as represented alpha-numerically and graphically. In different areas of use there arise specific kinds of Geo-Information Systems. GIS signifies the Technology, the Products and the Services to provide -> Geodata.
- GIS Analysis
Concering a -> GIS the Analysis signifies the core of the Functionality of a GIS; this Functionality allows to generate new Information and to analyse and formulate Relationships between spatial Phenomena. Tools of the GIS Analysis are e.g. -> Buffers and -> Netzwork Analysis.
- GML - Geography Markup Language
GML is a producer-independent, open concept to define geographic Objects and Data Schemes, which allows to model, to save and to transport geographic Information. GML is a Specification of the OGC based on the -> XML-Technology. The GML-Specification for Version 2.x determines only Simple Features (Point, Line, Area). New aspects in GML Verision 3.0 are complexe Geometries, spatial and temporal -> Reference Systems, -> Topology, Physical Units, -> Metadata, -> Raster Data and Default Styles for Features and Raster Visualization.
- GML Profile
A GML-Profile allows the Reduction of the constructs, defined in the -> GML Specification, on a Subset of Elements needed for a concrete Data Schema. Besides definition of Data Schemes a GML Profile is used to ensure a higher Performance, simpler Implementation and a better Reuse when developping Software Components; also distinct User Groups can profit from a better -> Interoperability.
- Graph Theory
The Graph Theory is a Part of the algebraic -> Topology, used to formulate and analyse Relations between Entities. Concerning the spatial Data Storage Systems the Graph Theory makes it possible to create topological -> Data Models and to formulate Conditions for Consistence.
- Graphic Primitives
A Graphic Primitive is a basic Element, which can be used to create a Drawing like a Point or a Line. A Graphic Core System defines e.g. Graphic Primitives like Point, Polyline, Symbols and Text.
- Hierarchy
A Hierarchy is a formal System, whereby each Element has a higher-ranking Element (except the Root Element). Each Element can have one or more lower-ranking Elements (except the lowest Level of Hierarchy). Hierarchies can be represented by Tree Structures very well and are therefore popular in Informatics because of their clear Structures. As thematic or spatial Hierarchies they are used for Data Modelling and for Data Storage in -> GIS Systems.
- Import (Interface)
Import is the Process to read Data (File) which was generated (-> Export) by another Computer System or Program. This kind of Software is called an Interface.
- Integrity
Integrity is existant, if Data don't have any formal and semantic Contradictions with the concrete Object they are representing. Such Data are also called "consistent". They are free of Redundance. Also the Completeness, Absence of Contradictions and Correctness of Data, stored in a -> Database, is encluded.
- Interface
Interfaces are needed to access saved Data (internal Data Interfaces) and/or to exchange Data (external Data Interfaces). The Exchange takes place in the most cases via standardized -> Data Formats, sometimes also via open internal Formats. The term is used for the Hardware, the Software and the Data and Applications in the -> GIS context.
- Interoperability
Interoperability signifies the possibility to integrate different Data in a single Process. Herefore Syntax and -> Semantics of the Data have to be provided by the user in a unified Form.
- Layer
A usable Separation of a -> Dataset, which contains in general Elements of a certain Theme. The Separations are related on a common Coordinate System and they allow the Analysis and Integration across the different Themes. This facilitates a logical, Theme-based Separation of mapped Information and is therefore the basis of the Layer Concept.
- Metadata
Metadata signify the System-internal Data of User Data stored in -> Databases and similar Systems; they are used to administer the User Data (Data describing Data). Metadata in -> GIS describe Properties, Definitions, Source, Validity, Accurateness, Usage of Datasets on different Levels of Aggregation.
- Network Analysis
A basic Group of -> GIS-Analysis Functions, based on linear Phenomena, which are used to compute and determine Relations between Entities. Examples are Shortest Path (Best Path), the Search for the next Neighbour (Best Locations), the computation of a Minimal Tree or the solution of the Travelling Salesman Problem. Basic for this group of Analysis Functions is the correct mapping of topological Relations; hereby mathematical methods of the -> Topology and -> Graph Theory are used.
- Object Class
An Object Class is a logical Classification of individual Objects having uniform Properties and Structures, which can be treated and processed using the same Methods. Classes can contain Sub-Classes, or they themselves can be Sub-Classes of other Classes (Object-oriented Programming!).
- Projection (Mapping)
A Projection signifies a Transformation Model for geometric Projections (e.g. by constructions, by computations or by optics). This is done by a mathematically defined Instruction, e.g. from spherical Coordinates (Surface of Earth) into a planar -> Coordinate System (Mapping). Common are the -> UTM Projection and the the Gauss-Kruger Projection.
- Quality
Quality is the totality of Properties of an Entity (Product, Service) concerning its ability to fulfil defined Preconditions. Basic Quality Properties of -> Geodata are Accurateness, Completeness, Actuality, Correctness and -> Consistence.
- Raster Data
Raster Data signify a kind of geometrical Representation of spatial Objects, where the Objects are split up equidistantly. This kind of Data Structure commonly uses quadratic Cells of equal Size (Matrix). In the Field of GIS there are commonly Image Data (Raster Data) with a spatial, geographic Relation. But there can be also any other numeric Information (e.g. Measurement Values), which are mapped onto a Matrix of Raster Elements.
- Spatial Relation
What is common to all -> GIS Applications, in the different fields using it, is the Spatial Relation. In Surveying the Spatial Relation is made by Definition of 2D or 3D Coordinates or by Instructions for construction, which is based on a definied -> Reference System and a primary Metrics. In other fields e.g. the Administration Statistics or in Business Mapping the Spatial Relation is based on very different facts.
- Reference System
A geodetic Reference System determines for a Position in 2D and Height as well the geodetic -> Datum (Origin of Coordinates, Orientation, Scaling, Form Parameters) as well as the Coordinate Mapping (-> Projection). Commonly the Reference System is defined by Set of -> Fixed Point of Geodesy. The common World-wide Reference System is called WGS84.
- Semantics
The Semantics is the theory of the meaning of linguistic constructions like words or sentences. The term comes from the Linguistic, but can also be used for Programming Languages and -> Data Models. The Semantics of a -> Geo-Object is commonly given by the accordance to a distinct Type or a distinct Class of Objects.
- Shape File
A Shape File is a Data Format defined by the ESRI Company to decribe and save -> Geodata. Besides the shp-File itself to save the Geometry Information, a shx-File to save the Index Information for the Geometry and a dbf-File to save the -> Attributive Data are generated.
- SQL - Structured Query Language
SQL is the Standard Query Language used in Relational Database Management Systems (RDBMS). SQL was defined for the first time as Standard by ANSI as SQL-1 in 1986. The current Standard is SQL:1999 (former term was SQL-3), which can be used on all Hardware Platforms.
- SVG - Scalable Vector Graphics
SVG is a Language on basis of-> XML to represent Vector Graphics in the WWW, defined by the Adobe Company. SVG was designed as platform- and browser-independent, open Markup Language, in collaboration between all important enterprises in the field of Browser, Graphics and Multimedia.
- Table
A Table is the possibility of Relational -> Databases to organize Data in Rows and Columns, whereby each Row represents an individual Entity, a so called -> Dataset or an Object, and whereby each Column represents a single so called Field or an -> Attribute Value.
- TIN - Triangulated Irregular Network
TIN is a Form irregular Tesselation based on Triangles and is used to represent correlated spatial Data, which are based on a Set of irregularly scattered Points. A TIN is often used for -> DEMs as method to generate a digital Terrain Representation from Point Data in a -> Vector Data Model.
- Topography
Topography is the term for all natural and anthropogene Objects on the Surface of the Earth (e.g. Forest, Stretches of Water, Houses, Streets etc.) and of the Relations between these.
- Topology
The Topology is a part of Mathematics which treats such Properties of geometric Entities, which stay invariant when projecting them using a distinct mathematical Operation. The metric circumstances are not of importance; only the mutual arrangement of geometric Entities in Space is concerned.
- Transformation, of Coordinates
The Coordinate Transformation is a Process of converting Coordinates from one -> Coordinate System to another. Common Transformations are Similarity Transformation, the Affine Transformation and the projective Transformation.
- Transformation, of Documents
Concering -> XML the Transformation is an conversion of XML Documents into other XML Documents or Text Formats.
- UTM Projection - Universal Transverse Mercator Projection
The UTM Projection is a conforme -> Projection, which was evented by the Mathematician Gauss. Geometrically it can be interpreted as a transversale Mercator Projection, i.e. a Cylinder is put transversally over the Earth Sphere. The perimeter of this Cylinder is smaller than the perimeter of the Earth along the Meridian, i.e. the Cylinder intersects the Earth Sphere. Along the both Meridians of these intersections the Projection conserves the Distances, with growing distance the aberration is growing. To map the whole Earth, this Cylinder must be moved systematically each 6 Degrees. In this way 60 stripes each of 6 Degrees arise. A rectangular -> Coordinate System is put onto this Zonal System, where its Abscissa is defined by the Central Meridian (Easting) and where its Ordinate is defined by the Equator (Northing).
- Vector Data
Vector Data are a -> Date Model, which is based on the representation of geographic Objects by cartesian Coordinates and is used commonly to represent linear Elements. Each Element is represented by a set of Coordinates, which define its shape. Basic types of Vector Data are Point, Line and Area (Simple Features).
- XML - Extensible Markup Language
XML is an open Standard of the W3Cs, which was desinged for the Definition, the Validation and the Exchange of Documents in the WWWW. XML is a Markup Language like HTML, but in XML a new kind of Markup Language can be defined to the needs of a certain task. Extensions can be defined either via Document-Type-Definitions (DTD) or via an XML Schema Definition (XSD), which is itself an XML Document.
MensorGIS Version 1.1.6, 2012/09/19