Unit AM4 Basic analytical operations
Type of Data Four simple datasets are used for these examples including 3 vector and at least one raster data file. Each file should generally overlap the region of the other files so that comparison operations can be done in the exercises:
- points - several dozen points roughly grouped together
- lines - a simple network of lines would be ideal
- areas - one or more polygons
- raster - with some simple grouped classes, not too noisy and similar in appearance to points, lines or areas.
Specific Examples All examples in this instance of the training are from the North Carolina demonstration dataset shapefiles and grids.
- points - bus stop locations - busstopsall.shp
- lines - stream network - streams.shp
- areas - lakes - lakes.shp
- a single point-like feature class - facility.grd
- road linework - roadsmajor.grd
Buffering a Multiple Point Shapefile
- open GIS application
- add shapefile or raster layer to the map view
- zoom to the extent of the layer
- select buffer geoprocessing tool
- enter required parameters and options:
- input layer - the layer that the buffer operation will be applied to
- output layer - the new file that will be created and include the buffer features.
- distance - the distance from the input features that the buffer will be created at
- options - including the option to dissolve the resulting features by merging the buffer features together instead of retaining the individual buffer lines of overlapping buffer perimeters.
Exercise using QGIS
This exercise uses the above method as it applies directly in QGIS. Other projects will be welcome to add their own example exercises as well.
TODO: Add screenshots
- Launch QGIS
- Load the data layer. Using menus at top of screen select LAYER -> Add Vector Layer
- Press Browse button
- Navigate to the folder holding the sample datasets and select busstopsall.shp and press Open button
- QGIS will automatically zoom to the extent of the bus stop features
- Run the buffer process from the menu: TOOLS -> Geoprocessing Tools -> Buffer(s)
- Set the Input vector layer to busstopsall
- Enter Buffer distance of 200. This will be 200 metres.
- Set the Output shapefile by pressing Browse button. Navigate to the data folder and enter the new filename as busstops_200m_buffer.shp. Press Save button to select that filename.
- Press OK button to run the process.
- After running, the system asks Would you like to add the new layer to the TOC? select Yes and the resulting shapefile will be added as a layer in your map view.
- Buffer(s) window remains open. Press Close to close the window.
- Reorder the layers so the resulting buffer polygons layer is on the bottom of the layer stack. Click and drag the busstops_200m_buffer.shp layer to beneath busstopsall.
- notes about what the student should notice about the results...