When displaying a map it is not always necessary to show a complete set of all layers and map feature types. The name of displaying variant – “Theme” suggests desirability of thematic choice of displayed features. For example, when working only with parcels, feature type “Building” and the whole layer “Municipal Economy” can interfere with the work. Those layers and feature types which are not to be displayed in the given theme should be simply deleted from the set of the theme's layers and feature types.
It should be understood that removing a layer or feature type from the theme means that this map component should not be displayed within this theme. If it becomes necessary to display the removed layer or type later, it can always be included into the theme again by selecting it from map components list. That is why operations of removing a component from the theme are not “dangerous”, they are reversible.
This situation is absolutely different from the one when layers and feature types are removed from the map. Removing a component from the map leads to irrevocable lose of data about all features of this component.
Later, in the chapter 14 “Cataloged themes”, subsection “Work layers of a theme”, work layers of theme will be considered. Deletion of such layers or of their feature types from the theme also results in irrevocable lose of features because work layers, in contrast to map layers, are actually contained in the theme rather than only displayed in it.
For working with a list of layers during theme browsing the menu command Theme+Layers or the button 
is used. The window “Layers of theme” shown at figure 12-7 is opened.
Figure 12-7. Window “Layers of theme”
It is evident that this window is similar to navigation windows described in chapter 3 “GDB Structure”. Actually, the window “Layers of theme” plays the role of a substitute of a navigation window, which is required because the browsed theme is not included into the hierarchic tree of GDB components, thus it is impossible to reach this theme in the navigation window. However, there are two essential peculiarities of the window “Layers of theme”:
Hierarchic pane of this window contains not all the tree of GDB structure, but only a branch describing the browsed theme, its layers and feature types.
GDB menu and the menu Tools are not present in the window “Theme layers”, the set of commands of the menu Edit is reduced compared with the analogous menu of the navigation window.
The window “Layers of theme” are subordinate with respect to the map browser window. Commands performed in the window “Theme layers” lead to changing display of the browsed theme (as soon as the browser window becomes active). If the map browser window is closed, its subordinate window “Layers of theme” will be closed simultaneously.
 |  |
