3.1. Buffer operations

We will now focus on the analysis and manipulation of line shapefiles. To do so, let’s consider only the roads_clip shapefile. You can turn-off all the other layers in the Layers panel to have a more compact visualization of the data.

../_images/3_roads_network.PNG

3.1.1. Single buffer

A very common operation with line shapefiles is the buffer, which allows to create an area within a specified distance from features. Note that in QGIS a buffer can be done also around point or polygon shapefiles. To create a buffer, click on Vector->Geoprocessing Tools->Buffer and specify the input parameters as follows:

  • Input layer: the roads_clip layer
  • Distance: the desired distance (in our case 10m). Note that you can also specify the unit of measure
  • Segments: the number of line segments to be used to approximate a quarter circle when creating rounded offsets (in our case 5)
  • Buffered: the path and the name of the output vector layer. Note that if left empty a temporary layer will be created

../_images/3.1_buffer.PNG

This will create a buffer area around our roads layer; if you zoom on your map, the result should look the following.

../_images/3.1_buffer_result.PNG

3.1.2. Multi-ring buffer

You can also create multiple buffers around the same features, within a specified distance.

To select the above function, we introduce here a very powerful instrument in QGIS: the Processing Toolbox. To add it to your window, go to View->Panels and tick “Processing Toolbox panel”. It should appear on the right side of your screen; this panel contains all the functions of QGIS, and in particular, the search bar is very useful to find the function you need.

../_images/3.1_processing_toolbox.png

In this case, you can search for “Multi-ring” and select the function Multi-ring buffer (constant distance). The input parameters are:

  • Input layer: the roads_clip layer
  • Number of rings: in our case 3
  • Distance between rings: in our case 10m
  • Multi-ring buffer (constant distance): the path and the name of the output vector layer. Note that if left empty a temporary layer will be created
../_images/3.1_multi_ring_buffer.PNG

This will create three buffer areas around our roads layer; if you zoom on your map, and if properly styled, the result should look like this:

../_images/3.1_multi_ring_buffer_result.PNG