Transcript Chapter14

Chapter 14
Analyzing Networks
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Copyright © 2006 by Maribeth H. Price
Outline
• Learning the function and terminology of
simple networks
• Understanding different types of networks
• Performing tracing analysis on networks
• Understanding how networks are
constructed
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Copyright © 2006 by Maribeth H. Price
Geometric networks
• Built inside a
feature dataset
• May have many
participating feature
classes
• Requires ArcEditor
or ArcInfo to build
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Copyright © 2006 by Maribeth H. Price
Network components
• Composed of edges and junctions
junctions
edges
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Copyright © 2006 by Maribeth H. Price
Network structure
Geometric network
is composed of
feature classes
Logical network
consists of tables
describing network
relationships
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Copyright © 2006 by Maribeth H. Price
Types of networks
Transportation Networks
Material moves as it wills
Utility Networks
Material flow dictated by
network geometry and
sources/sinks
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Copyright © 2006 by Maribeth H. Price
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?
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Copyright © 2006 by Maribeth H. Price
Network tracing
• Tracing solvers used to find solutions to
network problems
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Flags and barriers
Junction
flag
Edge
flag
Junction
barrier
Edge
barrier
• Flags indicate points
of interest (start, end,
stops)
• Barriers stop flow
through a feature
• Types should match
when solving a
problem
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Copyright © 2006 by Maribeth H. Price
Network Utility Analyst toolbar
Establish flow
Solve
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Copyright © 2006 by Maribeth H. Price
Finding paths
• Place flags and barriers
• Solve
Path with fewest edges
Copyright © 2006 by Maribeth H. Price
Default cost is
number of edges
traversed
Path with construction
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Finding shortest paths
• Use weights to override default cost
Find shortest path with
distance weight
Shortest path with three
stops Visited in order that
flags are placed
Copyright © 2006 by Maribeth H. Price
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Setting weights
• Analysis options
• Set for junctions or
edges
• Edge weights have
direction
• Usually need both
directions
Possible weights: Distance, travel time, wait at stop lights,
voltage or pressure drops, etc.
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Copyright © 2006 by Maribeth H. Price
Viewing flow directions
• Flow must be
established for utility
networks
• Flow direction
symbols can be
viewed and changed
• Set view scale to
hide arrows at
smaller scales
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Copyright © 2006 by Maribeth H. Price
Finding connected
• Find features
connected to or
disconnected from
the flagged feature
Water lines supplied by an
intake gallery
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Copyright © 2006 by Maribeth H. Price
Finding loops
Flag
Loop
Flow
• Used to find places
with indeterminate
flow
• Primarily used for
utility networks
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Copyright © 2006 by Maribeth H. Price
Directional tracing
• Find Upstream
– Trace the flow from a
feature to its source
• Trace Downstream
– Find the area
disrupted by a line
break
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Copyright © 2006 by Maribeth H. Price
Tracing with accumulation
• Uses default cost
(edges) or set
weights
• Returns total cost
associated with
found trace
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Copyright © 2006 by Maribeth H. Price
Find Common Ancestors
Probable
break
• Finds common
source for a set of
flags
• Use to locate
possible line break
from a set of
service calls
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Copyright © 2006 by Maribeth H. Price
Advanced analysis
• Avoid certain
features when
tracing
• Trace only on
unselected features
to avoid certain
streets
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Advanced analysis
• Return selection
• Use statistics to
find length of
connected water
lines
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Network analysis options
General options
• Tracing on selected
or unselected
features
• Inclusion of features
with indeterminate
flow
• Flag/barrier
snapping
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Copyright © 2006 by Maribeth H. Price
Results options
• Return result as
drawing or as a
selection
• All features or
those stopping
trace
• Return edges,
junctions or both
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Copyright © 2006 by Maribeth H. Price
Weight filters
• Use to exclude
certain weights
from analysis
– Screen out short
stop sign waits from
longer traffice light
waits
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Copyright © 2006 by Maribeth H. Price
Building networks
1
2
3
Simple edges—
Edges may have junctions
only on their endpoints
1
Complex edges—
Edges may have junctions
between their endpoints
Useful for query and
management, such as a water
main with many laterals
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Copyright © 2006 by Maribeth H. Price
How to build a network
• Ensure network features are topologically
valid and inside a feature dataset
• Create new network for the feature dataset
– Specify network layer
– Simple or complex edges
– Assign weights
Requires an ArcEditor or
ArcInfo license.
To build a road network
using your textbook data,
see “Building a simple
network” in the Skills
Reference section.
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Copyright © 2006 by Maribeth H. Price
Tools for managing networks
• Domains and subtypes
– Used to establish network attribute codes
• Pipes can only be 3-in, 6-in, or 12-in
• Default sizes and flow rates for different types
• Connectivity rules
– Define which features can connect to each
other and how
• T-valve must connect to three pipes
• 6-in line must connect to 3-in line through a
coupler
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Copyright © 2006 by Maribeth H. Price