Imagery can be integrated into a Geographic Information System (GIS) in several ways. Aerial photography is most often used by local, regional, and state government departments and agencies as a "backdrop" in a GIS to add context to vector (i.e., points, lines, polygons) data, providing a familiar frame of reference on which to highlight additional features. This imagery can clearly depict both land use and land cover characteristics.
In addition to providing additional context to support existing data, aerial photography is also used as a basemap, to support the development of additional data layers. Road center lines (RCL), impervious surfaces, and parcel boundary layers are often generated with the support of aerial photography.
Multi-spectral imagery can also be used in GIS. Instead of a traditional photograph that has been scanned, multi-spectral imagery contains digital information about the intensity of different colors of light (i.e., blue, green, red, infrared) recorded by the camera when the image was taken. Feature extraction tools are often used by GIS technicians to support the semi-automated classification of multi-spectral imagery, techniques which are effective due to the digital color information recorded in the imagery. Multi-spectral imagery has historically been captured by satellites but is increasingly being captured from aerial platforms (airplanes, blimps).
Scanned images (photos, documents, etc.) can also be integrated within a GIS environment. These images are not usually displayed as a layer on the map but are used to provide information about features that are already displayed (e.g., a deed for a property, a picture of a manhole cover).
