Geographic information system
A geographic information system (GIS) is typically defined as a computer software package designed to facilitate the analysis and display of geographically referenced spatial data by providing four general capabilities:
- Data input (encoding)
- Data management (i.e. archival, storage, query and retrieval)
- Statistical analysis (both basic data analysis and methods unique to spatial analysis)
- Output (display and input into other software)
All four of these functions involve interactions between the software system and the user, and most modern GIS packages are designed to allow the user to display the data and results associated with each function inside the program (i.e. most packages include a visual display and a graphical user interface, or GUI). GIS is primarily used to analyze spatial data acquired from cartographic records or remote sensing imagery, although GIS could theoretically be used to analyze any type of multidimensional data. [1]
Geographic information systems are a tool utilized by a wide variety of disciplines including resource management, conservation, asset management, cartography, market analysis, logistics, real estate, defense, emergency management, and transportation.
GIS Data Types
Data within a GIS can be represented in two general formats - raster and vector. The type of analysis being conducted and the nature of the data themselves largely determine which format will be used. The basic guideline that rasters are useful when representing spatially continuous variables while vector files are useful for representing categorical variables, is helpful, but significant exceptions exist. More commonly, raster layers will be used in modelling or geospatial analyses, while vector layers will be used in mapping and geographic analyses.
Raster Data
Raster data organizes information in a grid with a single attribute value assigned to each pixel, or cell. While grid cells are typically square, specific applications may call for the use of rectangular or other cell shapes.
Vector Data
Rather than a grid, the spatial positions of the data in a vector layer are stored as a series of nodes for each polygon, line, or point (a single node). By linking each polygon/line/point feature to an attribute table, vector data can contain numerous attributes per feature.
GIS and Remote Sensing
Because much of the spatial data used in GIS is based on remotely sensed images, the software systems designed for GIS and those designed for the processing of remotely sensed images are intimately related, and many of the major GIS packages include at least basic image processing capabilities, and image processing applications vice versa.
GIS software packages
As with many other software applications, both proprietary systems and open source systems are available. The majority of the proprietary systems are limited to the Microsoft Windows operating system, while the open source systems tend to work with several different OS types.
ArcGIS
ArcGIS is the primary GIS platform developed by Environmental Systems Research Institute, Inc. (ESRI). It is the most commonly used GIS software.
Notes
- ↑ Jensen, J. R. (1996) Introductory Digital Image Processing: A Remote Sensing Perspective. Prentice Hall Series in Geographic Information Science. Clarke, K. C. (ed.). Prentice Hall, Upper Saddle River, New Jersey, United States. 316 p.