Multiple Criteria Overlay Analysis in QGIS

Objective

• Identify areas to build new parking facilities to reduce bicycle theft.
• Criteria for site selection:
  • Must be in a bicycle theft hotspot.
  • Within 50 meters of a bicycle route.
  • Not within 50 meters of existing bicycle parking.

Data Used

• Bicycle infrastructure data for Westminster Borough, London City.
• Three vector layers:
  • Cycling Route (Line data)
  • Cycle Parking (Point data)
  • Shapefile of Westminster Borough
• Raster of cycling theft heatmaps

Steps in QGIS

Step 1: Open and Prepare Data

• Open QGIS and load the datasets.
• Change the color of necessary inputs for better visualization.

Step 2: Extract Hotspot Areas

• Use Raster Calculator to extract areas with high cycle theft.
• Criteria: Values above 12 on the theft heat map.
• Result: Boolean map with values 0 and 1.
  • 1 indicates hotspots (theft count > 12).

Step 3: Convert Raster Hotspots to Vector

• Use Polygonize tool to convert the Boolean raster map to vector format.
• Check the attribute table for values 1 (targeted hotspots).
• Use Extract by Attribute to isolate vectors with value 1.

Step 4: Create Buffers

• Create buffers for cycling routes and existing parking spots:
  • Distance: 50 meters
• Vector Geometry > Buffer: Apply to both cycling routes and parking spots.

Step 5: Intersection

• Use Intersection tool under Vector Overlay to find intersecting areas:
  • Input: Hotspot areas and route buffer.
  • Result: Vector layer showing intersection of hotspots and route buffers.

Step 6: Difference Operation

• Use Difference tool to subtract parking buffer from the intersection result:
  • Input: Intersection layer
  • Overlay: Parking buffer
• Result: Final polygons indicating most appropriate proposed parking spots.

Conclusion

• Final output shows proposed parking spots meeting all criteria.
• Temporary layers are not saved permanently; only the final result is saved.
• Encouragement to like, share, and subscribe to the channel.