Hong Zhang The Hong Kong Polytechnic University oceanzhhd@gmail and Zhilin Li

1. The 24th International Cartographic Conference Santiago, Chile ∙ November 15-21, 2009 Structural Hole Analysis for FormingHierarchical Road Network Hong Zhang The Hong Kong Polytechnic University oceanzhhd@gmail.com and Zhilin Li The Hong Kong Polytechnic University lszlli@inet.polyu.edu.hk

2. 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

3. Road as blood vessel in city (a): Hong Kong (b): Jeddah (http://www.spacesyntax.com/) (c): “The Image of City” (Kevin Lynch, ****) City vs Human body Network & Flows vs Blood vessel & blood

4. (c): Retail location Road impact our lives (a): Road and regional development (b): road and urban design

5. 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

6. Representation and Modelling(1) Fig. 3: a sample street network of London

7. Representation and Modelling Fig. 3: a sample street network of London

8. Properties • Fractal • Small-world • Scale-free • Self-organized • Hierarchical Fig. 5: Hierarchies emerged from traffic flow distribution (Adapted from Jiang 2009)

9. Road structure and human behaviours • Spatial cognition • Navigation • Path selection • Traffic flow • Location • Real estate develop • Pollution • Crime • ……

10. Limitations of current study (a) Observation window (Hillier and Iida 2005) (c) Navigation (Rosvall et al. 2005) (d) flow dimension and flow capacity (Jiang 2008) (b) Facilitating sensors

11. Objective Develop new techniques for Forming hierarchical road network

12. 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

13. 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 (c) Egocentric or personal network (a) Complete network

14. 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

15. Three simple ego networks (a) complete ego-network (b) ego-control network (c) ego-passive network

16. alter1 alter1 alter1 1 ego ego ego alter2 alter2 alter2 Link strength (a) complete ego-network (b) ego-control network (c) ego-passive network

17. Proportional Strength • Indirect Link Strength • Constraint • Aggregate Constraint • Centrality Rank (j∈ine), alter1 (j, q∈ine and q ≠j) ego alter2 Centrality Rank (a) An ego network

18. 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

19. b a c β α Road a Road b b a b Connectivity graph build stroke a c From road network to ego network • Build stroke • Produce connectivity graph • Derive ego network • Natural movement • Deflection angle

20. S7 S2 S78 S35 S35 S33 S10 S2 S2 S2 Theoretical illustration (a) A regular road network (b) Its connectivity graph (d) Its connectivity graph (c) An irregular road network Fig. 11: The sampled Road networks and their connectivity graphs

21. Experimental testing: data source (a) A map of Sweden (c) Its Connectivity graph (b) Sydost road map Note: Figure (a) and (b) are by courtesy of Bin Jiang

22. Top 1% Top 5% Top 20% The rest Experimental testing: results (a) Road hierarchies (b) Traffic flow distribution pattern

23. 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 constraints

24. 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/)

25. Thank you！Questions?