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QGIS Network Analysis Step by Step

QGIS Network Analysis: Complete Step-by-Step Guide

Network analysis in QGIS allows you to perform spatial analysis on connected linear features such as roads, rivers, utility networks, and transportation systems. This comprehensive guide will walk you through the entire process of conducting network analysis using QGIS’s built-in tools and plugins.

What You’ll Learn

  • Setting up your network data for analysis
  • Creating and configuring network datasets
  • Performing shortest path analysis
  • Calculating service areas and catchments
  • Analyzing network accessibility
  • Troubleshooting common issues

Prerequisites

  • QGIS 3.16 or later installed
  • Basic familiarity with QGIS interface
  • Vector layer data (roads, paths, or other linear networks)
  • Point data for origins and destinations (optional but recommended)

Step 1: Preparing Your Network Data

1.1 Load Your Network Layer

  1. Open QGIS and create a new project
  2. Click Layer → Add Layer → Add Vector Layer or use Ctrl+Shift+V
  3. Browse and select your road network shapefile or other vector data
  4. Click Add to load the layer into your project

1.2 Examine Your Data Structure

Before proceeding, examine your network layer:

  1. Right-click the network layer in the Layers Panel
  2. Select Open Attribute Table
  3. Look for these important fields:
    • Length/Distance fields (for cost calculation)
    • Speed limits (if available)
    • Road types or classifications
    • One-way restrictions (if applicable)

1.3 Data Cleaning and Preparation

Ensure your network data is properly prepared:

  1. Check topology: Go to Vector → Geometry Tools → Check Validity
  2. Fix gaps and overlaps: Use Vector → Geometry Tools → Fix Geometries
  3. Create unique IDs: If missing, add a unique identifier field
  4. Calculate lengths: Add a length field using Field Calculator with $length

Step 2: Installing and Activating Network Analysis Tools

2.1 Enable Processing Toolbox

  1. Go to View → Panels → Processing Toolbox
  2. The Processing Toolbox panel will appear (usually on the right side)
  3. Expand Network Analysis to see available tools

2.2 Install Additional Plugins (Optional)

For advanced network analysis, consider installing:

  1. Go to Plugins → Manage and Install Plugins
  2. Search for and install:
    • QNEAT3 (QGIS Network Analyst)
    • Network Analyst plugin
    • ORS Tools (OpenRouteService)

Step 3: Basic Network Analysis – Shortest Path

3.1 Shortest Path (Point to Point)

  1. In the Processing Toolbox, expand Network Analysis
  2. Double-click Shortest path (point to point)
  3. Configure the parameters:
    • Vector layer representing network: Select your road layer
    • Path type to calculate: Choose “Shortest” or “Fastest”
    • Start point: Click the map or enter coordinates
    • End point: Click the map or enter coordinates
    • Direction field: Select if you have one-way restrictions
    • Speed field: Select if you want time-based routing
    • Output layer: Specify output file location
  4. Click Run to execute the analysis

3.2 Interpreting Results

The output will show:

  • The optimal route as a line feature
  • Total distance and time (if speed data available)
  • Turn-by-turn directions in the attribute table

Step 4: Service Area Analysis

4.1 Creating Service Areas

Service areas show all locations reachable within a specified distance or time:

  1. Open Processing Toolbox → Network Analysis → Service area (from point)
  2. Configure parameters:
    • Vector layer representing network: Your road layer
    • Start point: Define the center point
    • Travel cost: Enter distance (meters) or time (minutes)
    • Strategy: Choose shortest path strategy
    • Output layer: Set output location
  3. Click Run to generate the service area

4.2 Multiple Service Areas

For concentric service areas (e.g., 1km, 2km, 3km):

  1. Use Service area (from point) tool
  2. In Travel cost, enter values separated by semicolons: 1000;2000;3000
  3. The result will show multiple buffer zones

Step 5: Advanced Analysis with QNEAT3 Plugin

5.1 Installing QNEAT3

  1. Plugins → Manage and Install Plugins
  2. Search for QNEAT3
  3. Click Install Plugin
  4. Restart QGIS if prompted

5.2 OD Matrix Analysis

Create origin-destination matrices:

  1. Processing Toolbox → QNEAT3 → OD-Matrix
  2. Configure:
    • Network Layer: Your road network
    • From-Point Layer: Origins (e.g., residential areas)
    • To-Point Layer: Destinations (e.g., hospitals, schools)
    • Optimization Criterion: Distance or time
    • Output: Choose matrix format
  3. Run to generate travel times/distances between all point pairs

5.3 Isochrone Analysis

Create time-based catchment areas:

  1. QNEAT3 → Iso-Area as Polygons (from Point)
  2. Set parameters:
    • Network Layer: Road network
    • Start Point: Center location
    • Size of Iso-Area: Time in minutes or distance
    • Interval: Step size for multiple isochrones

Step 6: Network Topology and Connectivity

6.1 Building Network Topology

For complex analysis, ensure proper network topology:

  1. Vector → Geometry Tools → Multipart to Singleparts
  2. Vector → Geometry Tools → Line Intersections
  3. Vector → Geometry Tools → Split with Lines (if needed)

6.2 Network Validation

Check network connectivity:

  1. Use GRASS → v.net.connectivity tool
  2. Identify disconnected components
  3. Fix gaps using editing tools

Step 7: Customizing Analysis Parameters

7.1 Direction and Restrictions

Handle one-way streets and restrictions:

  1. Add a Direction field to your network layer
  2. Use values like:
    • 0 for two-way
    • 1 for forward direction only
    • 2 for backward direction only
    • 3 for no traffic allowed

7.2 Speed and Cost Fields

Create realistic travel times:

  1. Add Speed field with speed limits
  2. Calculate Time field: "length" / "speed" * 3.6
  3. Use time field as cost in analysis

Step 8: Visualizing Results

8.1 Styling Network Analysis Results

  1. Right-click result layer → Properties → Symbology
  2. For routes: Use graduated symbols based on travel time/cost
  3. For service areas: Use categorized or graduated fills
  4. Add labels showing distances or times

8.2 Creating Professional Maps

  1. Use Project → New Print Layout
  2. Add map, legend, scale bar, and north arrow
  3. Include analysis parameters in text boxes
  4. Export as PDF or image for reports

Step 9: Common Issues and Troubleshooting

9.1 Connectivity Problems

Issue: “No route found” errors Solutions:

  • Check for gaps in network data
  • Ensure start/end points are close to network lines
  • Use Snap geometries to layer tool
  • Verify network topology

9.2 Performance Issues

Issue: Slow processing with large networks Solutions:

  • Clip network to study area
  • Simplify geometry if appropriate
  • Use spatial indexes
  • Consider using PostGIS for very large datasets

9.3 Projection Issues

Issue: Inaccurate distance calculations Solutions:

Step 10: Real-World Applications

10.1 Emergency Services Planning

  • Calculate response times from fire stations
  • Identify coverage gaps
  • Plan optimal facility locations

10.2 Retail Site Selection

  • Analyze customer accessibility
  • Calculate catchment areas for stores
  • Compare competitor locations

10.3 Transportation Planning

  • Optimize bus routes
  • Analyze traffic flow patterns
  • Plan infrastructure improvements

Best Practices and Tips

Data Quality

  • Always validate your network data before analysis
  • Ensure proper connectivity at intersections
  • Use consistent units throughout your analysis
  • Maintain attribute data accuracy

Analysis Setup

  • Start with simple point-to-point analysis before complex scenarios
  • Use appropriate coordinate reference systems
  • Test with small datasets first
  • Document your methodology and parameters

Result Interpretation

  • Consider real-world factors not captured in data
  • Validate results with local knowledge
  • Account for temporal variations (traffic, seasons)
  • Present results with appropriate uncertainty ranges

Advanced Topics

Integration with Web Services

  • Connect to routing APIs (OpenRouteService, GraphHopper)
  • Use live traffic data where available
  • Combine with demographic or business data

Automation and Scripting

  • Use QGIS Model Builder for repetitive tasks
  • Create Python scripts for batch processing
  • Integrate with external databases

Performance Optimization

  • Use spatial indexing for large datasets
  • Consider network preprocessing tools
  • Optimize attribute table structure

Network analysis in QGIS provides powerful capabilities for spatial analysis of connected systems. By following these step-by-step procedures, you can perform sophisticated routing analysis, accessibility studies, and location planning. Remember to always validate your results and consider the limitations of your input data.

For continued learning, explore the QGIS documentation, join user communities, and practice with different types of network datasets. The combination of QGIS’s built-in tools and third-party plugins makes it a comprehensive platform for network analysis needs.

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