What is GIS?
Glossary Terms
A geographic information system, or GIS, is a computerized framework for storing, managing, analyzing, and displaying geographic or spatial data. Characteristics of geographic features, known as attributes, are stored in data tables that also hold information about their geographic location. When these data sets, known as layers within a GIS, are placed over one another they create a model of the environment. As a result of the relationship formed between layers, a variety of analyses can be performed using the information contained within each dataset. GIS is more than just a map-making tool.
Figure 1 – Vector data.
GIS utilizes two types of spatial data: vector data and raster data. Vector data are represented as points, lines, or polygons. For example, schools (points), parks (polygons), and roads (lines) are all vector data (Figure 1). Raster data, in comparison, are composed of individual grid cells each assigned a unique value. Examples of this type of data include digital elevation models (DEMs), which can be used to create elevation contours or a hillshade like the one shown in Figure 2. DEMs can be used for a variety of analyses, such as for delineating watershed boundaries, important for water resource management. Aerial photographs and satellite imagery are also often raster data, which allows for analyses of landscape characteristics such as vegetative cover or land use.
Figure 2 – Raster data.
Critical to understanding GIS data layers are their metadata. Metadata is a document file that describes information about a data layer. A layer's metadata covers how the data was created, the accuracy and time relevance of the data, the source, and the meaning and codes of the attribute information. Although there are different formats in which to represent metadata, the U.S. standard for metadata was created by the Federal Geographic Data Committee (FGDC). Metadata that are considered compliant with FGDC guidelines include at least the following seven elements:
- Identification information, including information on how to cite the data and whom to contact about the data
- Data quality information, including the source of the data and how it was created
- Spatial data organization information
- Spatial reference information, including information on map projection and spatial extent
- Entity and attribute information
- Distribution information
- Metadata reference information
For more information on metadata, visit FGDC's Web site. All metadata provided in the Wai‘anae Ecological Characterization (WEC) GIS conform to FGDC metadata guidelines.
To learn more or view metadata about the specific data sets included in the WEC GIS go to the About the WEC GIS section.
