In many cases it is desirable that display of some layers and feature types depended on the scale of the map display. As an example, display of constructions on the city map may be examined. When displaying a map in a large scale it is convenient to single out displaying different construction types, such as buildings, pavilions, awnings, staircases, etc. using styles. When the scale is smaller construction features will be small and the difference in displaying styles loses its informative value and it is preferable to display all the constructions with one and the same style. With further zooming out separate constructions become practically indistinguishable and drawing them requires considerable time. That is why it is advisable not to display separate buildings and other small construction features using the small scale. Instead, you can switch to displaying bigger features, such as blocks of buildings.
Scale zones in ObjectLand are intended to control displaying of layers and feature types depending on the displaying scale. For creating and using scale zones, the user should perform the following operations:
Create a list of scale zones, that is, ranges of values of displaying scale for the present theme. For each value displaying characteristics of layers and feature types can be specified. For creating and changing scale zones the page “Scale Zones” of the theme property sheet is used (see chapter 15 “Properties of a theme and of its components”).
For some theme layers and/or feature types select displaying styles in every scale zone or indicate that in particular zones the present layer or feature type should not be displayed at all. For such actions the pages “Scale Zones” of property sheets of theme layers and feature types are used (see chapter 15 “Properties of a theme and of its components”).
Turn on the mode of using scale zones (the button 
in the standard toolbar of theme browser window or the box Use scale zones on the page “Scale Zones” of the property sheet of theme properties).
If the mode of using scale zones is turned on, the system selects the styles for displaying theme layers and feature types in the following way. The current value of displaying scale determines the scale zone to which this value belongs. For every theme layer displaying style specified for the current scale zone is used as displaying style of this layer. By analogy, displaying style of every feature type specified for the current scale zone is used instead of the usual displaying style for features of this type.
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