A Network Based Kernel Density Estimator
        Applied to Barcelona Economic Activities

Ecole Polytechnique Fédérale de...
Plan

• Goals
• Theory
• Methodology and Algorithms
• Barcelona case study
• Conclusion




EPFL – University of Strathcly...
Goals
• Goals
     – Create a network oriented density indicator to study cities design
     – Compare NetKDE indicator wi...
Theory
• Kernel Density Estimator (KDE):
     – Operates in Euclidean space
     – Weights events according to their radia...
KDE vs NetKDE




 KDE: For each raster cell, events inside a   NetKDE: For each raster cell, projected events
   radial b...
KDE vs NetKDE




 KDE: The Kernel function weights events   NetKDE: The Kernel function weights events
    according to t...
Methodology




EPFL – University of Strathclyde                 ICCSA, Geo-An-Mod 2010
Input data




                          »        Activities are stored in a shape file,
                          »      ...
Conversion




                                       » Files are exported into a PostGIS
                                ...
Activities projection


                            Projection


                                         » Activities are...
Activities projection


                            Projection




                  PostGIS


EPFL – University of Strath...
Calculation
                                       For each cell of the grid (represented by its
                         ...
Calculation
                                      The Script compute a Shortest Path Tree for
                            ...
Barcelona Case Study
• Material
     – Network: 11,000 edges
     – Activities: 166,000 economic activities listed by the
...
Kernel Density of activities
                                          Several activities
                                ...
Linear Density
                                                    Linear density of
                                     ...
NetKDE of activities
                                              Kernel formula
                                        ...
KDE of global betweenness
                                      Global betweenness
                                      i...
NetKDE of global betweenness
                                   For NetKDE of
                                   edges,
  ...
Conclusion
• This work proposes an innovative density indicator based
  on a road network, to better fit the urban constra...
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A Network Based Kernel Density Estimator Applied to Barcelona Economic Activities Timothée Produit, Nicolas Lachance-Bernard, Stéphane Joost

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A Network Based Kernel Density Estimator Applied to Barcelona Economic Activities Timothée Produit, Nicolas Lachance-Bernard, Stéphane Joost Ecole Polytechnique Fédérale de Lausanne, Switzerland LaSIG

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A Network Based Kernel Density Estimator Applied to Barcelona Economic Activities Timothée Produit, Nicolas Lachance-Bernard, Stéphane Joost

  1. 1. A Network Based Kernel Density Estimator Applied to Barcelona Economic Activities Ecole Polytechnique Fédérale de Lausanne, Switzerland LaSIG Timothée Produit, Nicolas Lachance-Bernard, Stéphane Joost University of Strathclyde, Glasgow, United Kingdom Urban Design Studies Unit Sergio Porta, Emanuele Strano Fukuoka, ICCSA, March 2010
  2. 2. Plan • Goals • Theory • Methodology and Algorithms • Barcelona case study • Conclusion EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  3. 3. Goals • Goals – Create a network oriented density indicator to study cities design – Compare NetKDE indicator with KDE indicator – Complete a proof-of-concept • Apply NetKDE to economic activities (points) • Apply NetKDE to network edges weighted by centrality indexes (polylines) • Technologies – Python Scripts, PostGIS Database, ArcGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  4. 4. Theory • Kernel Density Estimator (KDE): – Operates in Euclidean space – Weights events according to their radial distances from grid centroid • Network based KDE (NetKDE): – Operates in a Network Constrained space – Weights events according to the distance measured along this network EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  5. 5. KDE vs NetKDE KDE: For each raster cell, events inside a NetKDE: For each raster cell, projected events radial bandwith contribute to density along a network bandwith contribute to density evaluation. evaluation. EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  6. 6. KDE vs NetKDE KDE: The Kernel function weights events NetKDE: The Kernel function weights events according to their radial distance according to the distance measured along the network EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  7. 7. Methodology EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  8. 8. Input data » Activities are stored in a shape file, » Network is stored in a shape file, » Creation of a raster grid covering the extent of the network ArcGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  9. 9. Conversion » Files are exported into a PostGIS database » The raster grid is converted into points PostGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  10. 10. Activities projection Projection » Activities are projected on the nearest edge PostGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  11. 11. Activities projection Projection PostGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  12. 12. Calculation For each cell of the grid (represented by its centroid), the script imports the surrounding network and projected activities PostGIS Python Script EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  13. 13. Calculation The Script compute a Shortest Path Tree for the current raster cell, the NetKDE of point and the NetKDE of edges. PostGIS Python EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  14. 14. Barcelona Case Study • Material – Network: 11,000 edges – Activities: 166,000 economic activities listed by the Agencia de Ecologia Urbana in 2002 Network and activities • Computation – 926,000 raster cells, 10 meter resolution – 400 meter bandwith – 33 hours (Intel(R) Core(TM)2 Quad CPU, Q950 @ 3.00GHz, 2.99Ghz, 7.83 GB of RAM) Global • Zoom in on the center of Barcelona betweenness EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  15. 15. Kernel Density of activities Several activities can be located at the same place Bandwith = 400m Computed with ArcGIS EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  16. 16. Linear Density Linear density of activities = Nbr. Act./ Length of SPT Same scale EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  17. 17. NetKDE of activities Kernel formula • Activities: applied to activities projected on the KDE of network, activities Smaller patterns EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  18. 18. KDE of global betweenness Global betweenness is an indicator characterizing the centrality of an edge. Values of edges are generalized to the entire space. Computed with ArcGIS. EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  19. 19. NetKDE of global betweenness For NetKDE of edges, the inputs are the middle of edges and global betweenness. EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010
  20. 20. Conclusion • This work proposes an innovative density indicator based on a road network, to better fit the urban constraints on human mobility. • The processing using a PostGIS database is stable and fast. • Here are presented the first evaluation of the results • Current researches are related to: – Proofing NetKDE versus KDE (sensibility and geostatistical analysis) – Correlation analysis between Activitities and NetKDE centrality indicators – Research on other cities : Barcelona, Glasgow, Geneva, Bologna, Roma EPFL – University of Strathclyde ICCSA, Geo-An-Mod 2010

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