Welcome to Multi-Distance Buffer’s documentation!¶
Contents:
Functionality¶
The Multi-Distance Buffer QGIS plugin creates a multi-distance / multi-zone / multi-ring vector (memory) layer from an input vector layer and a set of distances.
The resulting layer consists of one (multi)polygon (“donut type”) for each buffer distance. The (multi)polygons do not overlap. The attribute table of the result layer will have two columns / fields named distance and inner, that contain the outer (maximum) distance and the inner distance for each (multi)polygon. For the innermost zone, the value of inner is not set. The resulting (memory) layer is added to the QGIS table of contents.
If 100 and 200 are provided as distances, the result layer will consist of two zones / bands / (multi)polygons - one will contain all areas that are within 100 units from the geometries of the input vector layer (including the geometries themselves) and will have its distance field set to 100; the other will contain all areas that are from 100 to 200 units from the geometries of the input vector layer and will have its distance field set to 200, and its inner field set to 100.
The buffer distances (decimal numbers) can be specified by the user in any order. The list will be kept numerically sorted by the Plugin.
Negative and 0.0 buffer distances are allowed for polygon layers only. Buffering a polygon with a negative buffer distance means shrinking the polygon and is also known as a setback.
Buffer distances can be added and removed in the dialogue using the Add, Remove and Clear all buttons. The Remove button removes the selected entries, while the Clear button removes all entries. The keyboard can be used to add individual buffer distances quickly (number followed by <enter>).
Fixed increment buffer distances can be added under the Add multiple tab, specifying the number of zones, the width of each zone and the start value.
A checkbox (Selected features only) can be used to choose to only buffer around selected features. If the user selects a layer with a selection, the default will be set to only use selected features. If there is no selection in the chosen layer, the default will be set to not only use selected features. The user can modify this behaviour by using the checkbox.
Three approaches to buffering are offered by the plugin¶
- Standard QGIS buffer operations
Will use five segments to represent a quarter circle for the buffer geometries in the result dataset.
- Segments to approximate (new in version 2.0/3.0)
The user specifies the number of segments to use for a quarter circle.
2 segments: 10 segments: 
- Maximum deviation (new in version 2.0/3.0)
The user provides the maximum radial deviation from the specified buffer distances in map units. The number of segments per quarter circle is calculated based on the buffer distance, and will increase with increasing buffer distances. In the illustrations, the buffer distances are 100 and 200.
max deviation 1: max deviation 10: 
Implementation¶
The buffer function of QgsGeometry is used, and the resulting buffer geometries are combined using the dissolve function of QgsGeometry.
The buffers are combined to form the multi-distance buffer using the symDifference function of QgsGeometry.
With the standard approach, buffers for all the distances used to be created using the buffer function of QgsGeometryAnalyzer. The buffer function of QgsGeometryAnalyzer did not support the specification of buffer accuracy (segments / arc vertex distance / maximum deviation), so the default of 5 segments had to be used.
Citation¶
Would you like to cite this plugin?
Tveite, Håvard. 2018. The QGIS Multi-distance buffer Plugin, Version 3.2.3. http://plugins.qgis.org/plugins/MultiDistanceBuffer/