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

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 City vs Human body Network & Flows vs Blood vessel & blood (b) Jeddah (http://www.spacesyntax.com/) (c) “The Image of City” (Kevin Lynch, 1960)

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

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. Graph Object Primal graphDual graph Characteristic points Axial line Stroke (70 degree) Named street Fig. 3: a sample street network of London Representation and Modelling(1)

7. Graph Object Primal graphDual graph ICN Segment Alternative chain Fig. 3: a sample street network of London Representation and Modelling(2)

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

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

10. 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

11. Objective Develop a new technique 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 (b) Complete network (c) Egocentric or personal 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. Proportional link strength (a) complete ego-network(b) ego-control network(c) ego-passive network alter1 alter2 ego 1 alter1 alter2 ego alter1 alter2 ego

17. Centrality Rank (j ∈ i ne ), (j, q ∈ i ne and q ≠j)  Proportional Strength  Indirect Link Strength  Constraint  Aggregate Constraint  Centrality Rank alter1 alter2 ego

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. From road network to ego network  Build stroke  Produce connectivity graph  Derive ego network  Natural movement  Deflection angle a b c α β a b c a b Road aRoad b build strokeConnectivity graph

20. 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 S35 S7

21. 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

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

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 constraint

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/)http://www.census.gov/geo/www/tiger/

25. Thank you ！ Questions?