Chapter 9
Network Analysis
Outline
•
•
•
•
•
What is networks?
Types of networks
Network analysis
Generic trace solvers
Utility trace solvers
What is networks?
• Any system of interconnected linear features is a network.
Geometric networks
• Built inside a feature
dataset
• May have many
participating feature
classes
• Requires ArcEditor or
ArcInfo to build
Network components
• Composed of edges and junctions
junctions
edges
Network structure
Geometric network is
composed of feature
classes
Logical network
consists of tables
describing network
relationships
Types of networks
Transportation Networks
Material moves as it choose
Utility Networks
Material flow dictated by
network geometry and
sources/sinks
Network problems
• Transportation
– What is the best path to
travel to sixteen delivery
locations?
– What is the likely service
area of a fire station based
on travel time?
– What is the shortest path
from point A to point B?
– What is the shortest path
which avoids narrow
streets?
• Utility networks
– If a valve fails, which
customers will be affected?
– If I have to close this pipe
for repairs, can I reroute
water through another path
to minimize service
disruption?
– How will contamination at
one location propagate
through the network?
– Which sewer lines serve
only residential customers?
Network analysis
Network tracing
• Tracing solvers used to find solutions to network
problems
Flags and barriers
Junction Edge
flag
flag
Junction Edge
barrier barrier
• Flags indicate points
of interest (start, end,
stops)
• Barriers stop flow
through a feature
• Types should match
when solving a
problem
Generic trace solvers
Finding paths
• Place flags and barriers
• Solve
Path with fewest edges
Path with construction
Finding paths
The path with the
fewest edges is the
default, but it is not
always the shortest
path.
Default cost is number of
edges traversed
To find the shortest
path, you must use
weights.
Path with fewest edges
Finding shortest paths
• Use weights to override default cost
Find shortest path with
distance weight
Path with fewest edges
What are weights?
• Weights are attributes associated with
features that describe the cost of
traversing the feature
– Edge costs might represent
• The distance of the edge
• The travel time along the edge
• The slope along a hiking trail
– Junction costs might represent
• The wait time at a traffic light or stop sign
• Pressure drop at a pipe junction
Creating weights
• Weights are created when the network is
established.
• If the weights do not already exist in the
network, you cannot use them.
Multiple stops
• You can find shortest paths with multiple stops.
The user specifies the order
of the stops and the solver
finds the best path.
Finding the best order of a
set of stops is a famous and
more difficult problem—the
traveling salesman problem.
Shortest path with three stops
Visited in order that flags are placed
Finding connected
• Find features
connected to or
disconnected from
the flagged feature
Water lines supplied
by an intake gallery
Utility trace solvers
Finding loops
• Used to find places
with indeterminate
flow
• Primarily used for
utility networks
Directional tracing
• Find Upstream
– Trace the flow from a
feature to its source
• Trace Downstream
– Find the area
disrupted by a line
break
Tracing with accumulation
• Uses default cost
(edges) or set
weights
• Returns total cost
associated with
found trace
Find Common Ancestors
• Finds common
source for a set of
flags
• Use to locate
possible line break
from a set of
service calls
Probable
break
Advanced analysis
• Avoid certain
features when
tracing
• Trace only on
unselected features
to avoid certain
streets
Advanced analysis
• Return selection
• Use statistics to
find length of
connected water
lines
References
• Price, M. (2013). Mastering ArcGIS (6th
ed.). McGraw-Hill
• Price, M. (2013). Mastering ArcGIS (6th
ed.). McGraw-Hill. Mastering ArcGIS, 6/e
Instructor Edition Chapter 9: PowerPoint
Notes and Figures