LINE DATA
The line is made up of an ordered set of coordinates linked in a chain
to represent the shape and length of a feature such as a road. The decision
to represent a feature as a line is scale dependent if the linear feature
occupies space at a 1:1 scale.
Other terms for line are ARC and VECTOR
The coordinates used to define the length and shape of a line are redefined
points
linked together. The terms that describe the points used to define a line
are NODE and VERTICE
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A NODE is located at each end of the line identifying the start
and end.
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VERTICES define the shape of the line and occupy the location between
the two nodes
NODES- three types:
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TRUE NODES: a true node is located at the intersection of three
or more arcs and forms the junction between the arcs.
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PSEUDO NODES: are located between two arcs linked together. In this
use, the node resides at the normal location of a vertice and acts to separate
the characteristics of two sections of the same line .
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DANGLING NODES: are located at the end of one arc defining it's
end and not linked to another arc.
EXAMPLES OF LINE FEATURES
NETWORKS
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Infrastructure networks
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Transportation networks - highways and railroads
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Utility networks - gas, electric, telephone, water
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Airline networks - hubs and routes
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Natural networks - River channels
ATTRIBUTES
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Direction of traffic, volume of traffic, length of road section, number
of lanes, time to travel
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Diameter of pipe, direction of gas flow
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Voltage of electrical transmission line, height of towers (nodes)
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Number of tracks, number of trains, gradient, width of most narrow tunnel,
load bearing capacity of weakest bridge
EXAMPLE OF NODE ATTRIBUTES:
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Presence of traffic lights, presence of overpass, names of intersecting
streets
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Presence of shutoff valves, transformers
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Attributes of some nodes (e.g. names of intersecting streets) link one
type of entity to another (nodes to links)
NETWORKS CAN BE USED
AS LINEAR ADDRESSING SYSTEMS
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E.G. if it is known that the block contains houses numbers from 100 to
198, house #124 would probably be 1/4 of the way along that link
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Go back to GER home pageAuthor: R. Douglas Ramsey Doug@nr.usu.edu