Imagery is a type of data that is useful for many GIS applications and is defined as any type of photograph. Normally photographs used for GIS projects consist of images gathered from a satellite or an aircraft. These can be photos that are printed on film or they can be taken with a digital camera and stored as digital images (NCSU Libraries). In addition, printed topographic maps that are scanned as digital images also constitute imagery.
In terms of the specific GIS data type, imagery is considered raster data. As such, all GIS images are made up of a grid of numbers that are arranged into rows and columns. Each grid is called a pixel and the pixels are assigned different numeric values. The different values assigned to the pixels typically represent quantities that identify things like elevation, slope gradient, or spectral brightness of an area (Verbyla, 1995). When all of the pixels are combined an image is formed.
Imagery is a data type that is extremely useful for GIS. It comes in many different types and it is able to show both large and small areas in varying levels of detail. This makes it versatile for a wide variety of different GIS projects and as such it is a common type of data for GIS projects.
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