How to find boundaries using wombling

Prior to wombling, you need to import a vector or raster data set, and for point data, check the spatial network and edit the network if necessary. If you want to womble on classified data, see How to detect boundaries on fuzzy classes.

1. Go to the "Data" menu and choose "Detect Boundary", and then "Wombling." Alternatively, choose "Detect Boundaries" from the pop-up menu that appears when you right-click a data set in the project window.

2. Proceed through the settings on the three tabs, General, Thresholds, and Other.

3. "General" tab

   1. Select the data set that you wish to analyze and a name for the new boundary.

   2. Choose which variables within the data set you would like to analyze. The default is to use all variables equally weighted.

      1. If you want to use only one variable, you can fill in the dot next to "Variable" (rather than Variable set) and select your variable.

      2. If you want to select a subset of variables, or if you want to weight the variables, choose the "Edit variable sets" button.

   3. If you would like to standardize the data prior to boundary delineation, click on the box at the bottom of the page. (If your data includes only one variable, this box will not appear).

4. "Thresholds" tab. You may set thresholds by entering a priori cutoff values or using the data set itself.

   1. Using a priori cutoffs

      1. Choose to set thresholds using "Information provided below."

      2. First, you need to decide what kind of boundary you want—crisp or fuzzy.

      3. Enter a percent of BLVs to use as boundary elements.

         • For crisp boundaries, choose the BLV threshold (default is 30%). Then, click on the "Other" tab of the dialog.

         • For fuzzy boundaries, choose threshold values for the overall boundary, and for the boundary core (default is 15%). If you are using polygon data, click on the "Other" tab of the dialog. Otherwise, skip to step 6.

   2. Using the distribution of BLVs (see Defining thresholds using histograms)

5. "Other" tab

   1. Specify the gradient angle thresholds you would like to use for connection.

   2. For polygon data only: Choose a dissimilarity metric from the pull down menu.

6. Click "OK" at the bottom of the dialog. If you checked the data standardization box, the next dialog will ask for a standardization method. Other sections describe the rationale and methods for standardizing data.

7. Next, a histogram (a BoundarySeer chart) of the BLVs for your data set will appear, and a dialog will ask you if you would like to view the boundary. You may view the boundary in a new or an existing map.