🎓 Mastering QGIS 💡 Weekly Insight - Week 47, 2024 📈 Quick Knowledge Boost Series
QField 3.4 “Ebo”: Geofencing and processing out of the box
Published by Mathieu.
QField 3.4 is out, and it won’t disappoint. It has tons of new features that continue to push the limits of what users can do in the field.
Main highlights
A new geofencing framework has landed, enabling users to configure QField behaviors in relation to geofenced areas and user positioning. Geofenced areas are defined at the project-level and shaped by polygons from a chosen vector layer. The three available geofencing behaviours in this new release are:
In addition to being alerted or informed, users can also prevent digitizing of features when being alerted by the first or second behaviour. The configuration of this functionality is done in QGIS using QFieldSync.
Pro tip: geofencing settings are embedded within projects, which means it is easy to deploy these constraints to a team of field workers through QFieldCloud. Thanks Terrex Seismic for sponsoring this functionality.
QField now offers users access to a brand new processing toolbox containing over a dozen algorithms for manipulating digitized geometries directly in the field. As with many parts of QField, this feature relies on QGIS’ core library, namely its processing framework and the numerous, well-maintained algorithms it comes with.
The algorithms exposed in QField unlock many useful functionalities for refining geometries, including orthogonalization, smoothing, buffering, rotation, affine transformation, etc. As users configure algorithms’ parameters, a grey preview of the output will be visible as an overlay on top of the map canvas.
To reach the processing toolbox in QField, select one or more features by long-pressing on them in the features list, open the 3-dot menu and click on the process selected feature(s) action. Are you excited about this one? Send your thanks to the National Land Survey of Finland, who’s support made this a reality.
QField’s camera has gained support for customized ratio and resolution of photos, as well as the ability to stamp details – date and time as well as location details – onto captured photos. In fact, QField’s own camera has received so much attention in the last few releases that we have decided to make it the default one. On supported platforms, users can switch to their OS camera by disabling the native camera option found at the bottom of the QField settings’ general tab.
Wait, there’s more
There are plenty more improvements packed into this release from project variables editing using a revamped variables editor through to integration of QField documentation help in the search bar and the ability to search cloud project lists.
Read the full 3.4 changelog to know more, and enjoy the release!
Some Tools And Workflows To Boost Your Productivity
Reclassify Raster Values for Simplification
Tool: Raster > Raster Calculator
Workflow: Simplify raster data by reclassifying values into categories, which is useful for land cover or zoning analysis.
Use Zonal Statistics for Raster Analysis
Tool: Raster > Zonal Statistics
Workflow: Calculate statistics (e.g., mean, sum) within vector polygons based on raster data, ideal for area-specific analysis.
Visualize Data with 3D Map View
Tool: View > New 3D Map View
Workflow: Create a 3D view for terrain, building footprints, and other spatial data, enhancing visualization for presentations.
Multi-Layer Selection for Complex Queries
Tool: Processing Toolbox > Select by Location
Workflow: Combine multiple selection criteria to isolate specific features across layers, useful for targeted data analysis.
Use Topology Checker for Spatial Integrity
Tool: Vector > Topology Checker
Workflow: Verify spatial relationships to maintain data accuracy, detecting overlaps, gaps, or dangles in line or polygon layers.
Batch Raster Conversion for Efficiency
Tool: Processing Toolbox > GDAL > Convert Format
Workflow: Convert multiple raster layers at once to a different format, a time-saver for large raster datasets.
Field Statistics for Quick Data Insights
Tool: Attribute Table > Field Statistics
Workflow: Generate basic statistics (e.g., count, min, max, mean) for attribute fields, providing an overview of data distribution.
Heatmap Plugin for Point Data Visualization
Tool: Plugins > Heatmap
Workflow: Use the heatmap plugin to visualize density of point data, enhancing spatial analysis in high-density areas.
Enhance Map Readability with Legend Layouts
Tool: Print Layout > Legend
Workflow: Customize map legends, adding symbols, labels, and grouping items for clear, professional-looking maps.
Create Point Grids for Sampling
Tool: Vector > Research Tools > Create Regular Points
Workflow: Generate a grid of points within a specified area for systematic sampling or surveys.
Vector Layer Buffering for Accurate Boundaries
Tool: Processing Toolbox > Buffer
Workflow: Create buffer zones around features, allowing accurate impact analysis for distances around points, lines, or polygons.
Add Labels to Lines with Curved Style
Tool: Layer Styling Panel > Labels
Workflow: Set labels to follow the curve of lines (e.g., rivers or roads), enhancing readability of labeled features.
Dynamic Grouping with Conditional Styling
Tool: Layer Styling > Rule-Based Styling
Workflow: Apply rule-based styling to show or hide features based on conditions, dynamically adjusting map visuals.
Calculate Solar Exposure for Land Analysis
Tool: Raster > Analysis > Terrain Analysis
Workflow: Generate solar radiation maps, useful for urban planning, agriculture, or energy studies.
Raster Mosaic for Seamless Coverage
Tool: Raster > Miscellaneous > Merge
Workflow: Merge multiple rasters to create a continuous mosaic, ideal for working with satellite imagery over large areas.
Set Scale-Dependent Visibility for Layer Control
Tool: Layer Styling > Scale-Dependent Visibility
Workflow: Display or hide layers based on zoom level, keeping maps uncluttered at different scales.
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Automate Batch Layer Export with Processing Models
Tool: Processing > Graphical Modeler
Workflow: Set up a model to export multiple layers in various formats, streamlining data sharing or reporting workflows.
Use Attribute Indexes for Faster Searches
Tool: Layer Properties > Fields > Index
Workflow: Index commonly searched fields to speed up queries and data filtering, especially useful in large datasets.
Set Transparency by Attribute
Tool: Layer Styling Panel > Transparency
Workflow: Vary transparency based on an attribute, creating subtle visual cues for data importance or density.
Automate Map Exports with Layout Manager
Tool: Print Layout > Layout Manager
Workflow: Create and save multiple layouts, automating exports with consistent formats across various projects.
Some QGIS Interview Questions & Answers:
Category: Geoprocessing Techniques
What is geoprocessing in GIS, and why is it essential?
Answer: Geoprocessing refers to a suite of tools used for manipulating spatial data, such as clipping, buffering, and intersecting layers. It’s essential for analyzing spatial relationships and creating new data based on existing datasets.
Tips for Responding: Describe how geoprocessing tools can streamline workflows and offer insights into spatial patterns or relationships.
How do you use the "Buffer" tool in QGIS, and what is it commonly used for?
Answer: The Buffer tool creates a zone of specified distance around features, which is useful for proximity analysis. In QGIS, find it under "Vector" > "Geoprocessing Tools" > "Buffer." It’s often used to analyze impact zones, like buffer zones around rivers or roads.
Tips for Responding: Provide examples, such as creating safety zones around hazardous sites, to show the practical uses of buffering.
Describe the process of merging vector layers in QGIS.
Answer: To merge layers, go to "Vector" > "Data Management Tools" > "Merge Vector Layers," select the layers to combine, and choose the output format. This tool consolidates multiple layers into a single one for easier analysis.
Tips for Responding: Mention how merging can simplify large projects or organize layers with similar data types, like merging different administrative boundaries.
What is the difference between the "Union" and "Intersection" tools in QGIS?
Answer: The "Union" tool combines two layers, preserving all features and attributes from both, while the "Intersection" tool only retains overlapping features and their attributes. Union is often used to combine datasets, whereas Intersection is useful for finding common areas.
Tips for Responding: Explain when to use each, such as using Union for inclusive mapping and Intersection for more targeted overlap analysis.
How do you dissolve polygons in QGIS, and why would you use this tool?
Answer: The "Dissolve" tool, under "Vector" > "Geoprocessing Tools," merges polygons based on shared attributes, creating a single feature where polygons overlap or are contiguous. It’s useful for simplifying data by removing boundaries.
Tips for Responding: Describe practical examples, like dissolving administrative boundaries into larger regions, to show knowledge of data simplification.
What is the "Clip" tool, and how is it applied in QGIS?
Answer: The Clip tool extracts a portion of a layer within the boundary of another layer, often used to isolate an area of interest. In QGIS, find it under "Vector" > "Geoprocessing Tools" > "Clip."
Tips for Responding: Mention applications, like clipping vegetation data to a project area, to highlight how clipping refines datasets for analysis.
Explain the concept of "Point-in-Polygon" analysis and its importance.
Answer: Point-in-Polygon analysis identifies which points fall within specific polygons, useful in tasks like determining whether points (e.g., homes or trees) lie within designated boundaries. QGIS supports this analysis through tools like "Select by Location."
Tips for Responding: Provide examples, such as analyzing properties within a zoning area, to show your understanding of spatial relationships.
Category: Advanced Spatial Analysis
What is raster overlay analysis, and how is it conducted in QGIS?
Answer: Raster overlay analysis combines multiple raster layers to analyze relationships, often for suitability modeling or impact assessment. In QGIS, use the Raster Calculator or overlay tools in the Processing Toolbox.
Tips for Responding: Explain any experiences using raster overlays, like combining soil and elevation data, which showcase your spatial analysis skills.
Describe the use of the "Zonal Statistics" tool in QGIS.
Answer: Zonal Statistics calculates statistics (like mean, sum, or count) of raster data within the zones defined by a vector layer, useful for summarizing data like elevation or temperature within specific regions.
Tips for Responding: Mention examples like calculating average elevation per administrative boundary to demonstrate data summarization techniques.
How do you perform network analysis in QGIS, and what are some common applications?
Answer: Network analysis in QGIS is done using the "QNEAT3" plugin or other network tools, which can solve shortest path, service area, or route optimization problems. Applications include finding optimal routes, accessibility, or service coverage.
Tips for Responding: Describe scenarios where network analysis is useful, such as emergency route planning or public transport access.
What is "viewshed analysis," and how is it conducted in QGIS?
Answer: Viewshed analysis identifies visible areas from a given point or elevation, often used for telecommunications or visibility studies. In QGIS, use tools like "Viewshed" within the Processing Toolbox with a Digital Elevation Model (DEM) layer.
Tips for Responding: Provide examples like analyzing line-of-sight for cell towers or observation points to show practical understanding.
Explain how to perform a suitability analysis using raster layers in QGIS.
Answer: Suitability analysis evaluates multiple criteria (like soil quality, slope, or distance) by overlaying and reclassifying rasters. In QGIS, use the Raster Calculator for weighting and combining layers based on suitability scores.
Tips for Responding: Mention specific suitability assessments, like selecting land for agriculture, to highlight applied knowledge in decision support.
How do you use "Sampling Points" in raster analysis, and why is this technique useful?
Answer: Sampling points extract values from a raster at specified locations, useful in validating model data or conducting fieldwork analysis. In QGIS, use "Raster" > "Sample Raster Values."
Tips for Responding: Explain any experience with sampling, such as comparing predicted vs. observed data, to highlight real-world applications.
Describe how to perform spatial autocorrelation analysis in QGIS.
Answer: Spatial autocorrelation analyzes the degree to which similar values cluster in space. In QGIS, tools like "Moran's I" from the Processing Toolbox measure autocorrelation, useful for clustering studies or pattern recognition.
Tips for Responding: Mention uses, such as analyzing disease spread or habitat clustering, to showcase applied understanding in spatial patterns.
What is kernel density estimation (KDE), and how do you perform it in QGIS?
Answer: KDE is a method for estimating the density of points over a surface, helpful for hotspot analysis. In QGIS, use "Kernel Density" from the Processing Toolbox.
Tips for Responding: Share examples, like crime hotspot analysis, to show how KDE supports pattern detection.
How do you apply supervised classification in QGIS?
Answer: Supervised classification assigns pixel values to categories based on training samples. Use plugins like "Semi-Automatic Classification" for tasks such as land cover classification.
Tips for Responding: Describe any classification projects, such as categorizing land use from satellite images, to demonstrate experience in remote sensing.
What is "Least-Cost Path Analysis," and how can it be used in QGIS?
Answer: Least-Cost Path Analysis finds the most efficient route between two points based on criteria like terrain or barriers. In QGIS, use the "Least Cost Path" plugin with cost rasters for applications like wildlife corridors.
Tips for Responding: Mention any projects where you optimized routes, showing applied problem-solving in spatial planning.
Stay tuned for next week's insights! 🗺️📈
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