Transcript Transmission Line Siting Model

Map Analysis
Procedures and Applications in GIS Modeling
Topic 19, Routing and Optimal Paths
Technical Overview
Procedures for Finding Optimal Routes and Corridors
Online book written by Joseph K. Berry
www/innovativegis.com/Basis/MapAnalysis/
published by BASIS Press
Transmission Line Siting Model (Hypothetical)
Existing Powerline
Goal – identify the best route for an electric
transmission line that considers various criteria
for minimizing adverse impacts.
Proposed
Substation
Houses
Criteria – the transmission line route should…
 Avoid areas of high
Roads
housing density
…prefer low housing density
 Avoid areas that are far from
roads
Sensitive Areas
…prefer close to roads
 Avoid areas within
or near sensitive areas
Elevation
…prefer far from sensitive areas
 Avoid areas of high visual
exposure to houses
…prefer low visual exposure
Houses
Routing and Optimal Paths (avoid high housing density)
PROPOSED
SUBSTATION
(END)
AVOID AREAS OF HIGH
HOUSING DENSITY
EXISTING
POWERLINE
(START)
(Least preferred)
(Most preferred)
MOST
PREFERRED
ROUTE
ACCUMULATED
PREFERENCE
SURFACE
HOUSES
HOUSING
DENSITY
DISCRETE
PREFERENCE
MAP
Housing Density levels (0-83 houses)
are translated into values indicating relative
preference (1= most preferred to 9=least
preferred) for siting a transmission line at
every location in the project area.
Step 1.
Accumulated
Preference from the
existing powerline to
all other locations is
generated based on
the Discrete
Preference map.
Step 2.
The steepest
downhill path from
the Substation over
the Accumulated
Preference surface
identifies the “most
preferred route”—
Step 3.
Most Preferred Route
avoiding areas of high
visual exposure
Siting Model Flowchart (Model Logic)
Model logic is captured in a flowchart where the boxes represent
maps and lines identify processing steps leading to a spatial solution
Within a single map layer
Among a set of map layers
Avoid areas of…
“Algorithm”
High Housing
Density …build on
this single factor
Far from Roads
In or Near
Sensitive Areas
High Visual
Exposure
“Calibrate”
“Weight”
Siting Model Flowchart (Model Logic)
Model logic is captured in a flowchart where the boxes represent
maps and lines identify processing steps leading to a spatial solution
Within a single map layer
Among a set of map layers
Step 1
“Algorithm”
“Calibrate”
“Weight”
Identify overall
Discrete Preference
(1 Good to 9 Bad rating)
Start
End
Step 2
Generate an
Accumulated
Preference surface
from the starting
location to
everywhere
Step 3
Identify the Most
Preferred Route
from the end
location
Start
End
Step 3
Step 2
Step 1
Step 1
Discrete Preference Map
…identifies the “relative preference” of locating a
route at any location throughout a project area
considering all four criteria
Calibrate
…then
Weight
[avoid areas of High Housing Density, Far from Roads,
In/Near Sensitive Areas and High Visual Exposure]
Discrete Preference Map
Least
Preferred
HDensity
(most preferred)
“Pass”
“Mountain” of
impedance
(avoid)
Most Preferred
RProximity
SAreas
VExposure
<click here to download an animated PowerPoint slide set describing calibration and weighting >
Step 2
Accumulated Preference Map
…identifies the “total incurred preference”
(minimal avoidance) to locate the preferred route from
a Starting location to everywhere in the project area
Accumulated Preference Map
(most preferred) “Pass”
(most preferred)
“Pass”
Splash Algorithm – like tossing a stick into a pond with waves emanating out
and accumulating preference as the wave front moves
<click here to download an animated PowerPoint slide set demonstrating Accumulation Surface construction>
Step 3
Most Preferred Route
…the steepest downhill path from the End over the
accumulated preference surface identifies the optimal
route that minimizes traversing areas to avoid
(most suitable)
Optimal Route
(most preferred) “Pass”
(most preferred)
“Pass”
<click here to download a short video (.avi) describing Optimal Path analysis >
Generating Optimal Path Corridors
…the accumulation surfaces from the Start to the End
locations are added together to create a total
accumulation surface—the “valley” is flooded to
identify the set of nearly optimal routes
(most preferred) “Pass”
(most preferred)
“Pass”
Optimal Corridor
<click here to download an animated PowerPoint slide set demonstrating Optimal Corridor analysis>
Example Results (Georgia Experience)
Combining alternative corridors identifies the
decision space reflecting various perspectives
Feature Article in GeoWorld, April, 2004
A Consensus Method Finds Preferred Routing
See www.geoplace.com/gw/2004/0404/0404pwr.asp
Calibrating Map Layers (using Delphi)
Model calibration refers to establishing a consistent scale from 1 (most preferred)
to 9 (least preferred) for rating each map layer…
1 for 0 to 5 houses
Fact
Judgment
…group consensus is
that low housing density
is most preferred
The Delphi Process is
used to achieve
consensus among
group participants. It
is a structured method
involving iterative use
of anonymous
questionnaires and
controlled feedback
with statistical
aggregation of group
response.
Within a single map layer (criterion) …the “Greens”
Delphi Process (Spreadsheet)
…structured method involving iterative use of
anonymous questionnaires and controlled feedback
1) Information on each data
layer is presented and
discussed by the group
2) Each participant identifies
their cut-off values
1=good to 9= bad (avoid)
3) Summary statistics are
computed and used to
stimulate discussion about
differences in opinions
…the process is repeated
until there is “acceptable”
consensus on the
CALIBRATIONS
Weighting Map Layers (using AHP)
Model weighting establishes the relative importance among
map layers (model criteria) on a multiplicative scale…
…group consensus is that housing density is very important (10.38 times more important than sensitive areas)
HD * 10.38
R * 3.23
SA * 1.00
VE * 10.64
The Analytical Hierarchy Process (AHP) establishes relative importance among
by mathematically summarizing paired comparisons of map layers’ importance.
Among a set of map layers (criteria) …the “Blues”
Conclusion (Technical Overview)
GIS-based approaches for siting electric transmission lines
utilize relative ratings (calibration) and relative importance
(weights) in considering factors affecting potential routes.
A quantitative process for establishing objective and
consistent weights is critical in developing a robust and
defendable transmission line siting methodology.
Objective, Quantitative, Predictable, Consistent, Defensible
References:
See www.innovativegis.com/basis, select , online book Map Analysis, Topic 19 “Routing and Optimal Paths”
See www.innovativegis.com/basis, select Column Supplements, Beyond Mapping, September 03, Delphi
See www.innovativegis.com/basis, select Column Supplements, Beyond Mapping, September 03, AHP
See www.geoplace.com/gw/2004/0404/0404pwr.asp, Feature Article in GeoWorld, April, 2004
“A Consensus Method Finds Preferred Routing” (Georgia Experience)