A buffer zone is a set of all map points which are located from the boundaries of this feature at a distance which does not exceed the specified value – width of the buffer zone.
The notion of a buffer zone is applicable to features of all spatial categories. For a point feature its buffer zone is a circle, for other spatial categories – a plane figure limited by segments of straight lines and circular arcs. At figure 18-15 examples of buffer zones of features are given.
a) features of different categories b) the same features with buffer zones
Figure 18-15. Examples of buffer zones of features
In ObjectLand an operation of building buffer zones for features selected in the map browser window is provided. As a result of this operation a new area feature coinciding with the buffer zone of original feature will be built for every selected feature. As usual, circular arcs are approximately simulated by polylines.
It should be noted that buffer zone for a point feature is built not around the feature symbol, but around a point in which the feature is located.
The width of the buffer zone for area, image and text features can be specified by a negative number. In this case the buffer zone includes the points lying inside the feature at a distance which is not less than the absolute value of the specified width of the buffer zone from the feature boundaries. For point and line features buffer zone of the negative width cannot be built.
To perform this operation it is necessary to switch to the mode Edit, select one or several features for which buffer zone should be built and perform the context menu command Create Buffer Zone. A dialog box “Creating buffer zone” shown at figure 18-16 will be opened.
Figure 18-16. Dialog box “Creating buffer zone”
The user should specify the layer and type to which the built features will belong. It is possible to select any area type displayed in the browsed theme. Besides, width of the buffer zone and the quantity of polygon points simulating the circle should be specified.
If it turns out that while creating buffer zones for several selected features these zones are intersected, the system actions will depend on the status of the checkbox Combine buffer zones. If this box is cleared, as shown at figure 18-15, b, individual features partially overlapping each other will be created. If this box is checked combining of overlapped features will be performed.
Creating buffer zones is performed after the button Perform is pushed.
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