A data model in geographic information system

Geographic Information System

A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...

s is a mathematical construct for representing geographic objects or surfaces as data. For example, the vector

Vector graphics

Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...

 data model represents geography as collections of points, lines, and polygons; the raster

Raster graphics

In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

 data model represent geography as cell matrixes that store numeric values; and the TIN

Triangulated irregular network

A triangulated irregular network is a digital data structure used in a geographic information system for the representation of a surface...

 data model represents geography as sets of contiguous, nonoverlapping triangles.

Representing three-dimensional map information

There are two approaches for representing three-dimensional map information, and for managing it in the data model

Data model

A data model in software engineering is an abstract model, that documents and organizes the business data for communication between team members and is used as a plan for developing applications, specifically how data is stored and accessed....

.

Vector-based stack-unit

Vector-based stack-unit maps depict the vertical succession of geologic units to a specified depth (here, the base of the block diagram

Block diagram

Block diagram is a diagram of a system, in which the principal parts or functions are represented by blocks connected by lines, that show the relationships of the blocks....

). This mapping approach characterizes the vertical variations of physical properties in each 3-D map unit. In this example, an alluvial deposit (unit “a”) overlies glacial till (unit “t”), and the stack-unit labeled “a/t” indicates that relationship, whereas the unit “t” indicates that glacial till extends down to the specified depth. In a manner similar to that shown in figure 11, the stack-unit’s occurrence (the map unit’s outcrop), geometry (the map unit’s boundaries), and descriptors (the physical properties of the geologic units included in the stack-unit) are managed as they are for a typical 2-D geologic map.

Raster-based stacked surfaces

Raster-based stacked surfaces depict the surface of each buried geologic unit, and can accommodate data on lateral variations of physical properties. In this example from Soller and others (1999), the upper surface of each buried geologic unit was represented in raster format as an ArcInfo Grid file. The middle grid is the uppermost surface of an economically important aquifer, the Mahomet Sand, which fills a pre- and inter-glacial valley carved into the bedrock surface. Each geologic unit in raster format can be managed in the data model, in a manner not dissimilar from that shown for the stack-unit map. The Mahomet Sand is continuous in this area, and represents one occurrence of this unit in the data model. Each raster, or pixel, on the Mahomet Sand surface has a set of map coordinates that are recorded in a GIS (in the data model bin that is labeled “Pixel coordinates”, which is the raster corollary of the “Geometry” bin for vector map data). Each pixel can have a unique set of descriptive information, such as surface elevation, unit thickness, lithology

Lithology

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...

, transmissivity, etc.).

See also

• Data model
  Data model
  A data model in software engineering is an abstract model, that documents and organizes the business data for communication between team members and is used as a plan for developing applications, specifically how data is stored and accessed....
  
  
• Data model (ArcGIS)
  Data model (ArcGIS)
  In ArcGIS, a data model a set of database design specifications for objects in a GIS application. A data model describes the thematic layers used in the applications ; their spatial representation ; their attributes; their integrity rules and relationships In ArcGIS, a data model a set of database...
  
  
• Data structure
  Data structure
  In computer science, a data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently.Different kinds of data structures are suited to different kinds of applications, and some are highly specialized to specific tasks...
  
  
• Georelational data model
  Georelational data model
  A georelational data model is a geographic data model that represents geographic features as an interrelated set of spatial and attribute data. The georelational model is the fundamental data model used in coverages....
  
  
• GIS

Further reading

• B.R. Johnson et al. (1998). Digital geologic map data model. v. 4.3: AASG/USGS Data Model Working Group Report, http://geology.usgs.gov/dm/.
• Soller, D.R., Berg, T.M., and Wahl, Ron (2000). "Developing the National Geologic Map Database, phase 3—An online, "living" database of map information". In Soller, D.R., ed., Digital Mapping Techniques ‘00—Workshop Proceedings: U.S. Geological Survey Open-File Report 00-325, p. 49–52, http://pubs.usgs.gov/openfile/of00-325/soller4.html.
• Soller, D.R., and Lindquist, Taryn (2000). "Development and public review of the draft "Digital cartographic standard for geologic map symbolization". In Soller, D.R., ed., Digital Mapping Techniques ‘00—Workshop Proceedings: U.S. Geological Survey Open-File Report 00-325, p. 43–47, http://pubs.usgs.gov/openfile/of00-325/soller3.html.