QGIS | Analyses and computations (raster data)
> Objective
This section addresses various computations and analyses with raster data
The students will learn how to compute hillshades, slopes and aspects
The students will learn how to perform area calculations
This section shows how to perform proximity analysis
This section shows how to perform multi criteria overlay analysis
This section shows how to do zonal statistics
This section addresses Boolean operators
The student will be introduced to analysis tools from the processing toolbox
> Index / Table of Contents
Introduction
Tutorial(s)
Hillshade, slope and aspect calculations
Area calculation
Proximity analysis
Multi criteria overlay analysis
Zonal statistics
Boolean operators
Analysis tools from the Processing Toolbox
QGIS installation
> Summary and Highlights
Introduction
Raster data can be used directly to analyse geographical data, but it might also be useful to first compute new data like area data. The following tutorials show some analyses and computations that can be done with raster data.
Tutorial(s)
Hillshade, slope and aspect calculations
Hillshades help to visualise the relief of a terrain by using light and shadows. The slope indicates the steepness of a terrain (in % or ° ) and the aspect specifies the orientation of the slope (in ° ).
Analyse a terrain by computing the hillshade, slope and aspect
QGIS Training manual: “7.3. Terrain Analysis”
Language(s): English
Chapters: follow along: calculating a hillshade, follow along: using a hillshade as an overlay, follow along: calculating the slope, try yourself calculating the aspect, follow along: calculating the aspect, follow along: using the raster calculator, try yourself more criteria, follow along: combining raster analysis results, follow along: simplifying the raster, follow along: reclassifying the raster, follow along: querying the raster, in conclusion, what’s next https://docs.qgis.org/3.10/en/docs/training_manual/rasters/terrain_analysis.html
Area calculation
The area of a surface can be calculated.
Area calculation per land cover class within the Kaziranga National Park
Ujaval Gandhi: “Calculating Raster Area (QGIS3)”/”Rastergebied berekenen (QGIS3)”
Language(s): English, Dutch
Chapters: overview of the task, get the data, procedure
EN: https://www.qgistutorials.com/en/docs/3/calculating_raster_area.html
NL: https://www.qgistutorials.com/nl/docs/3/calculating_raster_area.html
Area calculation per land cover class using the Corine land cover data of 2018
Hans van der Kwast: “QGIS raster analysis tools for calculating class surface area”
Language(s): English
Time: 4min 42s
Chapters: introduction (start-1:15), map canvas (1:15-2:22), unique values report (2:22-3:53), pie charts (3:53-end)
https://www.youtube.com/watch?v=gulqupCxA7w
Proximity analysis
Proximity analysis uses distances between different features (in this case, raster cells) to analyse geographical data.
Find pixels within a defined maximum distance from source cells
Hans van der Kwast: “Raster proximity analysis to determine the maximum distance to classes in QGIS”
Language(s): English
Time: 3min 29s
https://www.youtube.com/watch?v=ukmdmR7SDaU
Determine areas that are further than a specified distance from source cells
Hans van der Kwast: “Raster proximity analysis to the minimum distance to classes in QGIS”
Language(s): English
Time: 2min 15s
https://www.youtube.com/watch?v=Z9XhDl_19cQ
Multi criteria overlay analysis
Multi criteria overlay analyses help to identify the features that are the most suitable to a set of criteria (e.g. features close to water and shops, but far from highways).
Convert the vector data of Assam in India to raster data and identify the suitable areas for development
Ujaval Gandhi: “Multi Criteria Overlay Analysis (QGIS3)”/”Multi Criteria Overlay Analyse (QGIS3)”
Language(s): English, Dutch
Chapters: overview of the task, get the data, procedure
EN: https://www.qgistutorials.com/en/docs/3/multi_criteria_overlay.html
DU: https://www.qgistutorials.com/nl/docs/3/multi_criteria_overlay.html
Zonal statistics
Zonal statistics refer to statistical calculations (such as mean, median, sum) for a specific group of raster cells.
Perform zonal statistics by using a polygon layer with zones
Hans van der Kwast: “Zonal statistics in QGIS”
Language(s): English
Time: 5min 38s
Chapters: introduction (start-0:30), zonal statistics tool (0:30-3:36), raster layer zonal statistics (3:36-end)
https://www.youtube.com/watch?v=sHfXs_d8VLQ
Boolean operators
Boolean operators are simple words that can be used to select a set of features. Some examples are AND, OR and NOT.
Use a Boolean operator (AND) in the QGIS Raster Calculator to perform map algebra
Hans van der Kwast: “Map algebra with Boolean operator in the QGIS raster calculator”
Language(s): English
Time: 1min 33s
https://www.youtube.com/watch?v=UAcVehH6lI4
Create a Boolean raster in the raster calculator using comparison operators
Hans van der Kwast: “Create Boolean rasters with the raster calculator in QGIS”
Language(s): English
Time: 2min 21s
https://www.youtube.com/watch?v=lvkbQdQqcEs
Analysis tools from the Processing Toolbox
Raster analysis tools from the processing toolbox can also be used to perform spatial analyses.
Identify and extract informal settlements in the city of Johannesburg
Ujaval Gandhi: “Advanced raster analysis (QGIS3)”/”Gevorderde rasteranalyses (QGIS3)”
Language(s): English, Dutch
Chapters: overview of the task, get the data, procedure
EN: https://www.qgistutorials.com/en/docs/3/advanced_raster_analysis.html
NL: https://www.qgistutorials.com/nl/docs/3/advanced_raster_analysis.html
Spatial analysis by using the raster calculator from the processing toolbox and Graphical Model builder
Hans van der Kwast: “QGIS Processing Toolbox Raster Calculator & Graphic Modeler”
Language(s): English
Time: 12min 4s
Chapters: introduction (start-0:37), raster calculator (0:37-2:27), graphical modeler (2:27-9:48), running the model (9:48-end)
https://www.youtube.com/watch?v=7JCQQq9Yilg
> QGIS Installation
Do you still need to install QGIS? The QGIS installation and update section explains how to install QGIS on Windows and macOS.
Useful Links
Ujaval Gandhi (QGIS Tutorials and Tips website)
Hans van der Kwast YouTube channel
#QGIS, #Raster data, #Hillshade calculation, #Slope calculation, #Aspect calculation, #Area calculation, #Proximity analysis, #Multi criteria overlay analysis, #Zonal statistics, #Boolean operators, #Raster analysis tools from the processing toolbox
Hans van der Kwast. (2022, May 10). Raster Proximity Analysis to Determine the Maximum Distance to Classes in QGIS [Video]. YouTube.