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Hong Zhang
The Hong Kong Polytechnic Universityoceanzhhd@gmail.com
and
Zhilin LiThe Hong Kong Polytechnic University
lszlli@inet.polyu.edu.hk
Structural Holes for Forming
Hierarchical Road Network
The 24th International Cartographic ConferenceSantiago, Chile ∙ November 15-21, 2009
Outline
Why study road network?
Review of road network research Representation and modeling
Properties
Road structure VS human behaviors
Structural holes: concepts and methodology
Application of structural holes to road networks From road network to ego network
Theoretical analysis
Experimental testing
Conclusions
Road as blood vessel in city
(a) Hong Kong
City vs Human body
Network & Flows vs Blood vessel & blood
(b) Jeddah
(http://www.spacesyntax.com/)
(c) “The Image of City” (Kevin Lynch, 1960)
Road impact our lives
(a) road and regional development (b) road and urban design
(c) retail location
Outline
Why study road network?
Review of road network research Representation and modeling
Properties
Road structure VS human behaviors
Structural holes: concepts and methodology
Application of structural holes to road networks From road network to ego network
Theoretical analysis
Experimental testing
Conclusions
GraphObject Primal graph Dual graph
Characteristicpoints
Axial line
Stroke(70 degree)
Named street
Fig. 3: a sample street network of London
Representation and Modelling(1)
GraphObject Primal graph Dual graph
ICN
Segment
Alternativechain
Fig. 3: a sample street network of London
Representation and Modelling(2)
Fractal
Small-world
Scale-free
Self-organized
Hierarchical
Properties
Fig. 5: Hierarchies emerged from traffic flow distribution (Adapted from Jiang 2009)
Spatial cognition
Navigation
Path selection
Traffic flow
Location
Real estate develop
Pollution
Crime
……
Road structure and human behaviours
Limitations of current study
(c) Observation window (Hillier and Iida 2005)
(a) Navigation (Rosvall et al. 2005)
(b) flow dimension and flow capacity (Jiang 2008) (d) Facilitating sensors
Objective
Develop a new technique for
forming
hierarchical road network
Outline
Why study road network?
Review of road network research Representation and modeling
Properties
Road structure VS human behaviors
Structural holes: concepts and methodology
Application of structural holes to road networks From road network to ego network
Theoretical analysis
Experimental testing
Conclusions
Social network Structural hole is a concept rooted in social science.
Social sciences focus on structure and conceptualize social structure as a network of social ties (Nooy, et al., 2005).
examine the structure of the entire social group, or turn to the position of each individual in the local network.
(a) Social network
(b) Complete network (c) Egocentric or personal network
Structural hole and ego network
An ego network is defined as a road network consisting of a single actor (ego) together with the actors they are directly connected to (or alters) and all the links among them
Structural hole is an approach developed by Burt (1995) to define the positional status of each node in its ego network
The structural hole theory believes that in a social network, the individual’s advantage or power is based on his or her control over the spread of information, goods or services between his or her immediate neighbors, and the absence of a tie between either ego or alter and other alters would induce a structural hole
Three simple ego networks
(a) complete ego-network (b) ego-control network (c) ego-passive network
Proportional link strength
(a) complete ego-network (b) ego-control network (c) ego-passive network
alter1
alter2
ego
0.5
0.5 1
1
0.5
0.5
0.5
0.5
0.5
0.5
alter1
alter2 ego
0.5
0.5
1
1
alter1
alter2 ego
Centrality Rank
2
2'ij ij ij ij iq qj ne ne,
q
C p p p p p j i ,q i q i,q j
iij k
p1
(j∈ine),
qjiqij ppp '(j, q∈ine and q ≠j)
Proportional Strength
Indirect Link Strength
Constraint
Aggregate Constraint
Centrality Rank
i is nes
AC C s i ,s i
1 1i ne
i iss
CR s i ,s iAC C
0.
5
0.5
0.5
0.5
0.5
0.5
alter1
alter2
ego
Outline
Why study road network?
Review of road network research Representation and modeling
Properties
Road structure VS human behaviors
Structural holes: concepts and methodology
Application of structural holes to road networks From road network to ego network
Theoretical analysis
Experimental testing
Conclusions
From road network to ego network
Build stroke
Produce connectivity graph
Derive ego network
Natural movement
Deflection angle
a b
cα
β
a b
c
a b
Road a Road b
build stroke Connectivity graph
Theoretical illustration
Fig. 11: The sampled Road networks and their connectivity graphs
(a) A regular road network
(c) An irregular road network
(b) Its connectivity graph
(d) Its connectivity graph
S2
S10
S35
S33
S78
S2
S2 S2
S35
S7
Experimental testing: data source
(a) A map of Sweden (b) Sydost road map (c) Its Connectivity graph
Note: Figure (a) and (b) are by courtesy of Bin Jiang
Experimental testing: results
(a) Road hierarchies (b) Traffic flow distribution pattern
Top 1%Top 5%Top 20%The rest
Conclusions
Structural holes can be used for ranking street networks
There is a positive relationship between centrality rank and traffic flow
Weighted link strength and k-step aggregate constraint
Acknowledgements
This research is supported by the Hong Kong Polytechnic University and RGC of HK (PolyU5221/07E)
The data about Sydost highway network is provided by Bin Jiang
The San Francisco sampled road network is obtained from TIGER data of U.S.Census Bureau (http://www.census.gov/geo/www/tiger/)
Thank you！
Questions?
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