Weights of Evidence Extension for ArcView 3.0 /Spatial Analyst 1.0: Arc-WofE
Documentation for
Grouping Tool for generalizing Evidential Themes with Categorical Data
To use the Grouping Tool, select Generalize Evidential Theme from the Weights of Evidence menu. Select the Evidential Theme, the Class Field (field containing classes you want to generalize) and a Class Descriptor Field (field containing strings that describe the classes in the class field). Select the 'Define Groups' Generalization method (under 'Define Reclassifications'). Then click the 'Generalize' button. The following dialog box will be displayed. A description of each of the elements in the dialog is described below. Click on any of the elements to jump to its description.
The items you selected in the previous dialog are displayed at the top of the Grouping Dialog, as follows:
This is the evidential theme you selected in the previous dialog box. To change this selection, click the 'Close' button which returns you to the previous dialog. Select a new evidential theme and click 'Generalize' again.
The name of the field in the evidential theme's attribute table that contains the classes you want to generalize. It will also be used as the 'To' field for joining an associated table to the evidential theme's attribute table, if choose to use one.
The name of a field in the evidential theme's attribute table that contains strings describing the classes contained in the class field. If you didn't select a class descriptor field, <None> will be displayed.
Number of records to generalize
This reports the number of records in the evidential theme's attribute table. You can use this as reference in conjunction with the 'Remaining number of records:' reported at the bottom of the dialog. You will only be able to apply your generalization once all of the records have been grouped.
Number of classes to generalize
This reports the number of classes contained in the class field, which will the same or fewer than the number of records.
2. Associated table to join to attribute for queries
This combo-box lists any weights tables that you have calculated for an evidential theme (it looks for a field named "Class"). If you want to group your attribute records based on weights, contrast, etc., you can calculate the associated table. Once you select a table, it will be joined to the attribute table based on matching values between the "Class" field and the class field you specified above.
Type in a field name for a new field to which your generalized classes will be written. This field will be added to the evidential theme's attribute table and the generalized class values written to it. You need to type in a name before specifying any new class values.
If you would like to add text strings that describe your generalized classes to the evidential theme's attribute table, type in a name for a new descriptor field here. You need to type in a field name before specifying descriptive text for the generalizations. If no name is entered, no label field will be created, even if descriptive text has been included in generalization definitions (this could happen if you entered a field name and subsequently deleted it).
This is the first control to enter information about a new generalization. The field only accepts integers. You cannot enter anything to this line if you have not specified a class field name above.
Type in a string to describe your class integer, if you want. Data in this line is not required to create a generalization.
7. Group
Definition and Query Builder
The Group Definition text box and the query builder work in tandem. You can type the query that defines your group directly in the text box but most of the time it will be much easier to use the query builder to create your query. Click the query button to open the query builder. The fields in your attribute table, as well as the fields in an associated table, if you specified one, will appear in the left column. As you click on a field name, the values, in addition to zero, will appear for selection in the right hand column.
Unfortunately, there is not a way to define a group of records based on the occurrence of null values in the attribute table (cells are blank). This would be a problem if no training points fall within a class, or if all training points fall within a class. To include these classes, you can query on the #Points field (i.e. ([#Points] = 0)).
Once you have specified a class integer and a query to define the group of records/classes to generalize, the 'Add Generalization' button will be enabled. See the next section.
Click this button to add your group definition to the list of definitions in the display window. The values you entered in the input controls will be appended to the display of group definitions below, and they will be cleared from the input controls. The 'Add Generalization' button is enabled only when an integer has been specified as a new class value and valid query has been defined to group a set of records for generalization.
9. Generalization Display Window
Displays the generalization 'groupings' that will be applied to the evidential theme attribute table. A group definition or generalization will not be applied to an attribute table until it has been moved from the input controls to the display window.
To select one or more rows in the display, drag your mouse over the rows you want to select. Only contiguous rows can be selected at one time.
If you would like to edit one of the displayed rows, select it and click the 'Remove' button located below the display on the left side of the dialog. This will remove the generalization from the display window and display its components in their respective input boxes. You can edit any of the parts and re-add it to the display.
Displays the class value that will be written to the class field for those records associated with the generalization selection query.
Displays the descriptive string that will be written to the new class descriptor field for those records selected by the generalization 'grouping' query. None of the values will be written if no descriptor field name is specified above.
The query string that defines a group of records. The query is tested on the evidential theme attribute table before
The number of records in the evidential theme attribute table that are selected when the query string/group definition is applied. When the generalization is added to the display, this number is subtracted from the number of records remaining to be processed that is reported at the bottom of the dialog.
The number of unique classes contained in the class field that are represented by the records selected by the specified query.
The 'Remove generalization' button is enabled when one or more of the rows in the generalization display window are selected. Clicking the button removes the selected rows from the display. The last row only will be displayed in the input controls, so if you are removing rows to edit them, remove them one at a time, edit them and re-add before removing the next.
11. Number of records remaining
The initial 'Number of records remaining:' is the total number of records in the evidential theme attribute table. As you define queries to select groups of records for assignment to a new generalized class, and add them to the display window, the number of records is subtracted from the number of records remaining. When all of the records in the attribute table have been assigned to a group, the number of records remaining will be zero and the 'Generalize' button will be enabled.
Applies the generalization as defined by the new classes, new class descriptors and queries of existing classes to the attribute table. Each row in the generalization display window is processed in sequence: the query is applied to the attribute table and the specified class and class descriptor are written to new fields for the records selected by the query. The selection is removed and the next query is applied, until all of the rows have been processed.
Clicking the close button closes the dialog and unjoins any tables joined to the evidential theme attribute table.