Lecture 23 minilecture: A Brief Introduction to Network Analysis

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------Using GIS--
Introduction to GIS

• Lecture 23 (mini-lecture) A Brief Introduction
  to Network Analysis

Parts of the Network Analysis section of this
lecture were borrowed from a UC Berkeley GIS
Center Short Course, written by Anders Flodmark
slides are noted
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Network Analysis
------Using GIS--
Introduction to GIS

• Networks defined as a set of interconnected line
  entities, generally arcs, whose attributes share
  some common theme primarily related to flow.
• Arcs in a network must share the attributes
  necessary for analyzing these flows (speed
  limits, frictions, etc.)

Adapted from UC Berkeley GIS Center
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Network Arcs Can Have Direction
------Using GIS--
Introduction to GIS

• Directed - flows allowed to move in a single
  direction (down stream, one way street)
• Undirected - flows allowed in both directions
  (two way streets)

Adapted from UC Berkeley GIS Center
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------Using GIS--
Introduction to GIS
Basic elements of a network

• A network is a system of linear features
  connected at intersections and interchanges.
• These intersections and interchanges are called
  nodes

Arc
Node
The linear feature connecting any given pair of
nodes is called an arc.
Adapted from UC Berkeley GIS Center
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Network Attributes of interest
------Using GIS--
Introduction to GIS

• Attributes that can be attached to a network
• origin, destination coordinates
• shape point coordinates
• street name/highway number
• aliases on street name
• directionality one way traffic?
• classification freeway, arterial, collector,
  residential
• speed limit, congestion (impedance) or travel
  time
• traffic volume
• length driven length vs digitized length
• scenic value
• connectivity (turn tables)

Adapted from UC Berkeley GIS Center
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Network Problems
------Using GIS--
Introduction to GIS

• Path finding
• paths
• tours
• Allocation
• supply and demand
• impedance
• Spatial interaction
• accessibility
• interaction

Adapted from UC Berkeley GIS Center
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Path finding
------Using GIS--
Introduction to GIS

• Finding the shortest or least-cost manner in
  which to visit a series of locations in a
  network. The cost may be determined by distance
  or by travel-time or a combination of factors
  calculated as a cost value. Distance that factors
  in things that slow you down is known as
  functional distance
• Often the parameter that is minimized in path
  finding is travel time. This factors in things
  like topography, traffic volume, average speed,
  stops etc.

Adapted from UC Berkeley GIS Center
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Path finding
------Using GIS--
Introduction to GIS

• Computing best routes at the continental scale
  (e.g. how do I get from LA to New York?) is easy,
  because small variations in distance measures are
  relatively unimportant.
• At the intra-city level, the optimization
  criterion is travel time, which depends on legal
  restrictions (stop signs, traffic signals, one
  ways) and congestion (which varies by the
  minute), hence the margin of uncertainty in
  routing is far greater.

Adapted from UC Berkeley GIS Center
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This would not happen if Ponch and John had Path
finding software
------Using GIS--
Introduction to GIS
Gee, I dunno John, lets get off our bikes so we
can look at our big, cumbersome map, and try to
figure it out?
Ponch, theres a 4-12 going on at the video
arcade, whats the fastest way to get there?
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Location - Allocation
------Using GIS--
Introduction to GIS

• Allocation assigns portions of a network to a
  location based on predetermined criteria.
  Essentially an area of the network is assigned to
  be serviced or served by a facility at a given
  location. It is based on Supply, Demand, and
  Impedance.

Adapted from UC Berkeley GIS Center
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Allocation Assigns Portions of a Network to a
Center
------Using GIS--
Introduction to GIS
These street segments can be used to define a
service area
Adapted from UC Berkeley GIS Center
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Allocation Assigns Portions of a Network to a
Center
------Using GIS--
Introduction to GIS
Allocation analysis yields service areas for each
of these facilities that is, the areas they can
reach within a specified driving time.
Source http//www.geo.umass.edu/courses/geo594a/w
armup/warmup3/
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Allocation
------Using GIS--
Introduction to GIS
Adapted from UC Berkeley GIS Center
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Spatial interaction
------Using GIS--
Introduction to GIS

• Accessibility How Connected is a Node
• Accessibility is an aggregate measure of how
  reachable a location is from other locations.

Adapted from UC Berkeley GIS Center
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Accessibility
------Using GIS--
Introduction to GIS
Adapted from UC Berkeley GIS Center
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Usefulness of Network Analysis
------Using GIS--
Introduction to GIS

• Used by retailers in market studies for siting
  new facilities
• Used by utility company in managing their
  infrastructure water, sewer, power
• Used by consumers to get directions
• Used by agencies to map out service areas fire,
  police, public transportation facilities.