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 The following excerpt was taken from the Transportation Planning Handbook published in 1992 by the Institute of Transportation Engineers (pp. 102-103). The transportation system is represented by a network of lines; each road and transit route is drawn as a line on a map or overlay at the same scale as the zone map. The intersections of the transportation lines are called nodes. Each node is assigned a unique number, starting with a number somewhat greater than the highest zone number. . . . The two node numbers at the ends of any link identify that link. A roadway is defined by the links along its path. The links are stored in the computer according to their identifying node numbers. Transit routes are identified and stored in a similar manner, as the string or series of node numbers along the transit route. For transit routes operating on roadways, the string of node numbers identifies the roadway nodes traversed by the transit route. (p. 103) The characteristics of the roadway represented by each link are coded as attributes of that link. The attributes usually include the length of the link (in miles), the vehicle capacity of the roadway, and the speed or time of movement along the link. Depending on the computer program being used, other attributes of the link or activity along the link may also be coded, such as adjacent land use, character of the area in which the link is located, whether parking is permitted, and the classification of the facility that the link represents.
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