QGIS | Analyses and computations (vector data)
> Objective
This section addresses various computations and analyses with vector data
The students will learn how to perform network analyses
The students will learn how to compute line lengths
This section shows how to perform nearest neighbour analysis
The students will learn how to perform area calculations
This section shows how to determine percentages per class
The student will be introduced to analysis tools from the processing toolbox
This section show how to perform a height analysis with lines and AHN data
This section shows how to perform a population density analysis
> Index / Table of Contents
Introduction
Tutorial(s)
Network analysis
Line length calculation
Nearest neighbour analysis
Area calculation
Class percentages
Street intersection density
Analysis tools from the processing toolbox
Height analysis Population density analysis
QGIS installation
> Summary and Highlights
Introduction
Vector 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 vector data.
Tutorial(s)
Network analysis
Network analysis can be used to find distances, travel times and shortest paths between two locations.
Define the shortest and fastest path QGIS Training manual: “6.3. Network Analysis” Language(s): English Chapters: follow along: the tools and the data, calculate the shortest path (point to point), try yourself fastest path, follow along: advanced options, shortest path with speed limit, service area (from layer), in conclusion, what’s next https://docs.qgis.org/3.10/en/docs/training_manual/vector_analysis/network_analysis.html
Build a road network and define the shortest path between two points in the city of Washington DC Ujaval Gandhi: “Basic Network Visualization and Routing (QGIS3)”/”Basis netwerk visualisatie en routeren (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/basic_network_analysis.html NL: https://www.qgistutorials.com/nl/docs/3/basic_network_analysis.html
Find out the facility with the least travel distance from each address in the city of Washington DC Ujaval Gandhi: “Locating Nearest Facility with Origin-Destination Matrix (QGIS3)”/ “Dichtstbijzijnde faciliteit zoeken met Origin-Destination Matrix (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/origin_destination_matrix.html NL: https://www.qgistutorials.com/nl/docs/3/origin_destination_matrix.html
Define areas within 15-minutes of walking distance in the metro rail station data for Kochi, India Ujaval Gandhi: “Service Area Analysis using Openrouteservice (QGIS3)”/”Analyse Servicegebied met Openrouteservice (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/service_area_analysis.html NL: https://www.qgistutorials.com/nl/docs/3/service_area_analysis.html
Determine the travel times to a chosen location in the city of Bangalore, India Ujaval Gandhi: “Travel Time Analysis with Uber Movement (QGIS3)”/”Reistijd-analyse met Uber Movement (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/travel_time_analysis.html NL: https://www.qgistutorials.com/nl/docs/3/travel_time_analysis.html
Define the shortest path Erik Meerburg (3D geoinformation research group): “Urbanism GIS Course 16: Network analysis” Language(s): English Chapters: introduction (start-1:30), geofabric download website (1:30-2:32), OpenStreetMap (2:32-5:13), network analysis (5:13-9:01), open root service (9:01-end) https://www.youtube.com/watch?v=KW7EFDyl7eM
Line length calculation and statistics
Lines can also be analysed in QGIS. The length can be calculated and some statistics can be performed on them.
Computation of the total length of railroads in the United States Ujaval Gandhi: “Calculating Line Lengths and Statistics (QGIS3)”/”Lengten van lijnen en statistieken berekenen (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/calculating_line_lengths.html NL: https://www.qgistutorials.com/nl/docs/3/calculating_line_lengths.html
Nearest neighbour analysis
The nearest neighbour analysis allows to determine the features that are the closest to a given feature.
Determine the nearest populated place for each location where an earthquake happened Ujaval Gandhi: “Nearest Neighbor Analysis (QGIS3)”/”Analyse Nearest Neighbor (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/nearest_neighbor_analysis.html NL: https://www.qgistutorials.com/nl/docs/3/nearest_neighbor_analysis.html
Use QGIS spatial statistics within the Processing Toolbox QGIS Training manual: “6.4. Spatial Statistics” Language(s): English Chapters: follow along: create a test dataset, creating random points, sampling the data, follow along: basic statistics, follow along: compute statistics on distances between points, follow along: nearest neighbour analysis (within layer), follow along: mean coordinates, follow along: image histograms, follow along: spatial interpolation, try yourself different interpolation methods, in conclusion, what’s next https://docs.qgis.org/3.10/en/docs/training_manual/vector_analysis/spatial_statistics.html
Area calculation
The area of a surface can be calculated.
Calculate surface area of polygons Hans van der Kwast: “Calculate Areas of Polygons in QGIS” Language(s): English Time: 1min 32s https://www.youtube.com/watch?v=ca_yF7aGXKM
Compute area Erik Meerburg (Geogoeroe): “Oppervlakken berekenen” Language(s): Dutch Time: 13min 25s https://www.youtube.com/watch?v=PTux2E3p7vg
Compute total usable area of each building Erik Meerburg (Geogoeroe): “BAG: totaal gebruiksoppervlak per pand berekenen” Language(s): Dutch Time: 10min 15s https://www.youtube.com/watch?v=vEWzi-GhWVA
Class percentages
The percentage of features per class can be determined within polygons.
Derive percentage of land use within polygons from CORINE 2018 Hans van der Kwast: “Calculate percentage of land use per subcatchment in QGIS 3” Language(s): English Time: 17min 38s Chapters: introduction (start-1:20), style (1:20-2:15), catchment polygons (2:15-3:00), unique numbers (3:00-3:40), catchment area (3:40-4:30), more steps (4:30-5:15), exporting (5:15-6:35), expression (7:10-9:25), dissolve (9:25-11:50), intersect (11:50-12:40), fix geometry error (12:40-14:00), fix intersection error (14:00-end) https://www.youtube.com/watch?v=xfjg_jpgiTE
Derive percentage of land use using the field calculator Hans van der Kwast: “Calculate Percentage Land Cover per Subcatchment in QGIS” Language(s): English Time: 3min Chapters: introduction (start-0:20), calculate percentage (0:20-1:30), add class names (1:30-end) https://www.youtube.com/watch?v=U9ePqf1KXmE
Street intersection density computations
Street intersection density computations refer to determining the number of streets per area.
Calculate the street intersection density for the city of Chennai in India Ujaval Gandhi: “Calculating Street Intersection Density (QGIS3)”/”Dichtheid van straatkruisingen berekenen (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/calculating_intersection_density.html NL: https://www.qgistutorials.com/nl/docs/3/calculating_intersection_density.html
Analysis tools from the processing toolbox
The processing toolbox can also be used to perform spatial statistics. Basic statistics (e.g. mean, sum, median calculation) can be done, but also more advanced ones (e.g. nearest neighbour analysis).
Use QGIS spatial statistics within the Processing Toolbox QGIS Training manual: “6.4. Spatial Statistics” Language(s): English Chapters: follow along: create a test dataset, follow along: basic statistics, follow along: compute statistics on distances between points, follow along: nearest neighbour analysis (within layer), follow along: mean coordinates, follow along: image histograms, follow along: spatial interpolation, try yourself different interpolation methods, in conclusion, what’s next https://docs.qgis.org/3.10/en/docs/training_manual/vector_analysis/spatial_statistics.html
Height analysis
The height of walls can be analysed by using a vector file with lines and Actueel Hoogtebestand Nederland (AHN) data, which contains the elevation data of the Netherlands.
Height analysis based on lines and AHN data in Amsterdam Erik Meerburg (Geogoeroe): “Hoogte analyse kademuren in QGIS” Language(s): Dutch Time: 24min 53s https://www.youtube.com/watch?v=GrgbN3v1Asc
Population density analysis
The population density can be computed and analysed.
Population density analysis Erik Meerburg (Geogoeroe): “Is de Voorhof de dichtstbevolkte buurt van Nederland?” Language(s): Dutch Time: 3min 37s https://www.youtube.com/watch?v=fyQIj5kh9A4
> 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
Erik Meerburg (3D geoinformation research group) YouTube channel
Erik Meerburg (Geogoeroe) YouTube channel
#QGIS, #Vector data, #Network analysis, #Line length calculation, #Nearest neighbour analysis, # Area calculation, #Percentages, #Street intersection density, #Analyses tools from the processing toolbox, #Height analysis, #Population density analysis
Hans van der Kwast. (2019, February 14). Calculate percentage of land use per subcatchment in QGIS 3 [Video]. YouTube.