What Is GIS?

A Geographic Information System (GIS) represent a systematic integration of computer hardware, software, data and procedures designed to support the data capture, storage, management, updating, manipulation, analysis, and display of spatial data.

More simply, a GIS is a system that provides the ability to work with information that is referenced to the surface of the earth.

A GIS will specify three things:

  1. where each feature is geographically
  2. what each feature is
  3. what each feature"s relationship(s) are to other features on a map

The Figure below illustrates the key concept in GIS of overlays. A Geographic Information System allows geographic data layers to be overlayed onto of each other which can then allow for various analyses such as intersect, union, erase, and clip, to name a few.

Geographic data layers can contain either vector or raster data and may contain descriptive data such as attributes. A GIS can allow wildlife biologists and land managers such as yourself to conduct spatial analyses that can help answer applied questions. For example, using GIS, one can:

  1. Demarcate the boundary of protected areas when integrating field GPS coordinates
  2. Identify suitable habitat for wildlife species using remote sensing techniques combined with GIS analyses
  3. Perform least-cost path analyses
  4. Delineate watersheds and conduct flow accumulation analyses
  5. Identify and prioritize land best suitable for wildlife migration corridors
  6. Delineate the vegetation composition of habitat types within protected areas
  7. Identify areas prone to erosion

Suggested Readings on the Web (links require an Internet connection):

GIS Data

GIS data can be described as either spatial or descriptive.

Spatial data is defined as the data that relates to the geographic location or relationship of objects and features. These can be displayed as points, lines, polygons, or surfaces and represent cities, rivers, forests, or elevation. In GIS, spatial data are generally are in two formats; Vector and Raster.

Vector data, in the context of GIS, refers to a series of points, lines and polygons that have associated descriptive information (called attributes).

Points
example of towns from Addis Ababa to Goba

Lines
example of major roads in Ethiopia

Polygons
example of the Rift Valley Lakes

Raster data are displayed in a series of cells that form a grid pattern with continuous data over a geographic area. In GIS, these are called surfaces. In a surface, each cell has a value that is representative of the cell"s area (usually the mean value).

For example, elevation is often displayed as raster data called a Digital Elevation Model (DEM). Each pixel of a DEM contains the mean elevation for each cell. Precipitation, slope and population concentrations are also commonly displayed in raster formats.

A DEM of Ethiopia (left) is displayed in a raster surface with continuous data across the entire country. The raster cells form a grid, where each cell (right) has a value that represents the average elevation for area covered on the landscape.

Descriptive data are the characteristics that are associated with spatial data. In GIS, descriptive data are often referred to as attribute data.

There are three types of descriptive data:

GIS Components

There are six major components associated with successful GIS applications These are:

Data

  • Spatial data - raster, vector
  • Descriptive data
  • Data acquisition
  • Scale/Accuracy/Resolution
  • Projections/Coordinate systems

Software

  • ArcGIS software, Microsoft Excel, etc.
  • Analyses and computational capabilities
  • Map display

Hardware

  • Computer, monitor, hard drives
  • GPS units
  • Digitizer, scanner, printers

Procedures

  • Flow charting
  • Analyses
  • Programming
  • Field verification

Expertise

  • You and other users
  • On-line support

Documentation

  • Meta data
  • Flowcharts