Displayed theme can contain several map layers, and each layer can include several feature types. The filter condition described above is specified for one feature type and divides the features of this type into groups. One filter condition cannot refer to features of several types. On the other hand, it is possible to specify individual filter conditions for every feature type of the theme (or for some types only). Conditions for different types are specified independently of one another, each of them is used when displaying features of the corresponding type. A set of all filter conditions specified for different feature types of the theme is called theme filter.
When displaying a theme the user can choose if the filter of this theme should be turned on or not. If the filter is turned off, none of filter conditions for feature types is taken into account when displaying features, all the features of the types which are included into the theme are displayed in the theme, the style of displaying features is determined without taking filter into account according to the rules of inheritance described in chapter 10 “Feature displaying styles”. If the theme filter is turned on, all the filter conditions specified for feature types of the theme are taken into account.
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