Exercise 3 - Mapping landscape connectivity with all-pairs centrality
For this example, we will analyze ‘all-pairs’ rather than subset centrality.
Our example is based on the same data set of wolf habitat suitability in the Yellowstone region used in Exercises 1 and 2. This analysis may require more processing time to complete than previous exercises.
1) Hexmaps Tab – Once again, we can skip this step because we will use the same habitat5.hxn file created in Exercise 1.
2) Graphs Tab –
Refer to p. 18 of the Toolkit manual for a description of the Graphs Tab.
In Exercise 2, we created an edgelist input file named hab5dist.txt. In this exercise we will use this file again, as well as an additional file of conductance values.
Press the + tab above the upper box and add the file habitat5.hxn to the upper box (Hexmap Source File).
Set graph type as Edgelist - Conductance (Current Flow).
Set the Output file name as hab5cond.txt
Leave checked ‘No Data Value -9999’.
Press Run.
Examine the file hab5cond.txt in a text editor. Note how the edge values are the reciprocal of those shown in the first edgelist file we created (hab5dist.txt).
3) Connectivity Tab - Refer to p. 21 of the Toolkit manual for a description of the Connectivity Tab.
First analysis:
In the Connectivity Tab, set the Function as ‘Shortest-Path Betweenness Centrality’.
Browse and locate the graph file, hab5dist.txt.
Because we are not using a subset file, leave input file type as ‘Generic data’.
Browse and name the output file: hab5betweenness.tab.
Set 'probability value' to 0.02 (=2%), which is lower than the default sampling proportion of 5% and will result in faster completion of the function.
Press Run to run the analysis.
The progress of the analysis will be displayed in the ‘Output’ tab.
Second analysis:
In the Connectivity Tab, set the Function as ‘Current Flow Betweenness Centrality’.
Browse and locate the graph file, hab5cond.txt.
Because we are not using a subset file, leave input file type as ‘Generic data’.
Browse and name the output file: hab5currentflow.tab.
Set 'probability value' to 0.2, which is higher than the default error tolerance of 0.1 and will result in faster completion of the function.
Press Run to run the analysis.
The progress of the analysis will be displayed in the ‘Output’ tab.
4) Working with the CAT output files
Join the 2 output files to the to the HEX_ID field in the shapefile as described in previous exercises.
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