Interpolating Spatial Interaction Data

Transactions in GIS

Transactions in GIS, August 2011, Volume 15, Issue 4

Woo Jang and Xiaobai Yao

“Spatial interpolation has been widely used to improve the spatial granularity of data, or to mediate between inconsistent zoning schemes of spatial data. Traditional areal interpolation methods translate values of source zones to those of target zones. These methods have difficulty in dealing with flow data, as each instance is associated with a pair of zones. This study develops a new concept, flow line interpolation, to fill the abovementioned gap. We also develop a first flow line interpolation method to estimate commuting flow data between spatial units in a target zoning scheme based on such data in a source zoning scheme.

Illustration of proportions of units in the source zoning scheme overlapping units in the target zoning schemes

Illustration of proportions of units in the source zoning scheme overlapping units in the target zoning schemes

“Three models (i.e., areal-weighted, intelligent, and gravity-type flow line interpolation) are presented. To test the estimation accuracy and the application potential of these models, a case study of Fulton County in Georgia is conducted. The results reveal that both the areal-weighted and intelligent models are very promising flow line interpolation methods.”

Topology of Surfaces: Modelling Bridges and Tunnels in 3D-GIS

Computers, Environment and Urban SystemsComputers, Environment and Urban Systems, Volume 35, Issue 3, May 2011, Pages 208-216

Gerhard Gröger and Lutz Plümer

“Research highlights:

  • Extend an existing axiomatic characterization of surfaces embedded in 3D space without handles to handles, enabling the modeling of bridges and tunnels.
  • Topological specification of handle objects contributing to semantical-topological consistency (conditions to distinguish handle objects from non-handle objects topologically).
  • Provide an efficient method to differentiate between Jordan and handle cycles.
  • Specify conditions which avoid that editing operations on surfaces fail due to handles.

Bridges and tunnels are semantically meaningful objects in Geographical Information Systems (GIS), playing an important role in terms of reachability between locations. From a topological point of view, bridges and tunnels on surfaces are captured by the notion of a handle. In this paper, we extend an existing axiomatic characterization of 3D surfaces, which guarantees consistency between geometry and topology, to the case of handles. Furthermore, we present a method which verifies the occurrence of handles in surfaces, thereby contributing to the semantic-topological consistency in GIS. We close the gap between the global topological definition of handles in surfaces and the local definition of semantical handle objects in GIS – tunnels, bridges, arcades. Our method bases on a classification of cycles in two types. We give an efficient algorithm for discriminating both using standard methods from graph theory. This classification in addition contributes to the correctness of editing operations in GIS.”

MIT Researchers Create New Urban Network Analysis Toolbox

MITMIT researchers have created a new Urban Network Analysis (UNA) toolbox that enables urban designers and planners to describe the spatial patterns of cities using mathematical network analysis methods. Such tools can support better informed and more resilient urban design and planning in a context of rapid urbanization. “Network centrality measures are useful predictors for a number of interesting urban phenomena,” explains Andres Sevtsuk, the principal investigator of the City Form Research Group at MIT that produced the toolbox. “They help explain, for instance, on which streets or buildings one is most likely to find local commerce, where foot or vehicular traffic is expected to be highest, and why city land values vary from one location to another.”

MIT researchers create new Urban Network Analysis toolbox.

MIT researchers create new Urban Network Analysis toolbox. Image credit: MIT.

Network analysis is widely used in the study of social networks, such as Facebook friends or phonebook connections, but so far fairly little in the spatial analysis of cities. While the study of spatial networks goes back to Euler and his famous puzzle of Königsberg’s seven bridges in the 18th century, there were, until recently, no freely accessible tools available for city planners to calculate computation-intensive spatial centrality measures on dense networks of city streets and buildings. The new toolbox, which is distributed as free and open-source plugin-in for ArcGIS, allows urban designers and planners to compute five types of graph analysis measures on spatial networks: Reach; Gravity; Betweenness; Closeness; and Straightness. “The Reach measure, for instance, can be used to estimate how many destinations of a particular type — buildings, residents, jobs, transit stations etc. — can be reached within a given walking radius from each building along the actual circulation routes in the area”, said Michael Mekonnen, a course six sophomore who worked on the project. “The Betweenness measure, on the other hand, can be used to quantify the number of potential passersby at each building.”

The tools incorporate three important features that make network analysis particularly suited for urban street networks. First, they account for geometry and distances in the input networks, distinguishing shorter links from longer links as part of the analysis computations. Second, unlike previous software tools that operate with two network elements (nodes and edges), the UNA tools include a third network element — buildings — which are used as the spatial units of analysis for all measures. Two neighboring buildings on the same street segments can therefore obtain different accessibility results. And third, the UNA tools optionally allow buildings to be weighted according to their particular characteristics — more voluminous, more populated, or otherwise more important buildings can be specified to have a proportionately stronger effect on the analysis outcomes, yielding more accurate and reliable results to any of the specified measures.

The toolbox offers a powerful set of analysis options to quantify how centrally each building is positioned in an urban environment and how easily a user can access different amenities from each location. It introduces a novel methodology for tracking the growth and change of cities in the rapidly urbanizing world and offers analytic support for their designers and policymakers.

The UNA toolbox can be downloaded from the group’s website.

[Source: MIT press release]