To create a filter of some feature type of the theme it is necessary to create at least one filter group apart from three standard groups. Creation of a new group is performed using the menu command Edit+Add provided that the group list pane is active (i.e. a mouse click was performed in this pane). The system opens a dialog box “Filter conditions for new group”. Specifying condition will be described below. After the user determined the filter condition and pushed the button OK, the added group is included into the list of filter groups of the present feature type. The system assigns names to the groups being added: <Group 1>, <Group 2> and so on in the order in which they were created.
Another way of creating a new filter group is duplicating the group created earlier. To do this it is necessary to select the filter group in the list which condition is the most similar to the assumed condition of the group being created and then perform the menu command Edit+Duplicate. A group the filter condition of which coincides with the condition of the duplicated group will be created. The user will be able to change the condition later.
The menu commands Edit+Remove and Edit+Rename perform removing and renaming operations. Simultaneous removing of several selected filter groups is allowed.
The command Edit+Order allows changing the order of checking group conditions. In chapter 34 “Filters and their structure” it was shown that this order can be meaningful if the group conditions are not mutually exclusive. When the command Order is performed, a dialog box “Order of groups” shown at figure 37-2 is opened.
Figure 37-2. Dialog box “Order of groups”
The pane of the dialog box contains a list of all groups for which filter conditions are specified. The buttons Up and Down permit moving the selected group to a new place in the list.
It should be noted that position of groups in the list pane of the navigation window corresponds to the order of checking their conditions only in the case if the column name looks like this: =Group Description. Two other possible forms of the column name – +Group Description and –Group Description correspond to the position of groups in ascending or descending alphabetical order of their descriptions. Switching between modes of displaying a list of groups is performed by clicks on the column name but it doesn't affect the order of checking conditions.
To change the existing condition of filter group it is required to select this group in the list pane of the navigation window and perform the menu command Edit+Conditions. A dialog box “Filter conditions for group” shown at figure 37-3 will be opened. If one of the standard groups “True”, “False” or “Undefined” is selected, the command Edit+Conditions is disabled since the conditions for these groups cannot be specified.
Groups “True”, “False” and “Undefined” can be renamed, however, operations of removing, duplicating, changing the order and condition cannot be applied to them.
If the standard groups are renamed, the meaning of each of them can be defined by the sign by which the group is marked: 
– “True”, 
– “False” and 
– “Undefined”.
The command Edit+Filter Description allows the user to enter description (an arbitrary string) which will be displayed in the title of the list pane of the navigation window and in the legend window.
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