Wednesday, February 4, 2015

Calculate Spatial Importance of Road Network in ArcGIS

A recent study found that Random Walk algorithm can be utilized to rank spatial importance of road networks. The basic idea is that by simulating a person's random walking in a road networks, the road segments or interactions that have been walked through many times are considered spatially important. Such spatial importance of road networks is evidenced in their close correlation to some social-economic characteristics of surrounding urban areas structured by road networks, e.g., population density, job density, or even house prices. More details can be found at this article: The Random Walk Value for Ranking Spatial Characteristics in Road Networks.

An  ArcGIS Tool has been devised to implement this Random Walk simulation. 

Four functions are provided in this ArcGIS Tool:
  1. Construct graph object

    Open a road network shapefile in ArcGIS. Open Construct Graph Network tool in the ArcGIS tool box, select the road shapefile as the edge layer. The weight field can be any numerical attributes of a road network, such as width, design speed and etc. In the node layer field, select the nodes that will be included in the random walk simulation, such as bus stops. Select the X and Y coordination of the node layer, and define the output folder and network name. This tool will create a graph object.
    If you don't have specific road nodes or you want to include all the road junctions in the random walk simulation , you can create road nodes by adding a network dataset of the road shapefile in ArcGIS.
  2. Simulate random walk

    Open the Calculate Random Walking Value tool in the ArcGIS toolbox, select the created graph in the Network File field. Define the output folder, field name, threshold of loop value, weight, and simulation method of the random walk simulation. The definitions of those parameters can be found in the The Random Walk Value for Ranking Spatial Characteristics in Road Networks.

    Random walk simulation may take several minutes. After the calculation is done, you can import the calculated edge and node shapefile in ArcGIS. A wlk files recording the walking paths is also created in the defined folder.

  3. Visualize random walk paths

    You can visualize the simulated random walk paths in ArcGIS by using the Check Random Walking Paths tool. In the Check Random Walking Paths tool, select the created wlk file in step 3, define how many walking paths you want to check, and define the output folder if you want to visualize those walking paths as shapefiles.
  4. Calculate other network measures of road networks (using Networkx)

    This tool can also calculate other network measures such as PageRank, betweenness, closeness and etc. To do that,open the Calculate PageRank Value tool in the ArcGIS toolbox, select the create network graph in the step1, and define the output folder of the network calculation. The network measures will be saved in a table in the defined folder.

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