Site Selection: Multi-Criteria Suitability

This tutorial builds a suitability surface for siting a facility: you will filter candidate parcels with SQL, buffer the constraints, score each criterion, and combine everything into one map. It uses the Vector tools, the Raster tools, and the SQL Workspace.

1. Load your layers

Add at least four layers (see Adding Data):

• candidate parcels (polygons),
• constraint features, for example roads and protected areas,
• optional: a DEM or any raster you want to score against.

2. Filter candidates with SQL

Open the SQL Workspace and narrow the parcels to what your project actually allows:

SELECT * FROM parcels
WHERE zoning = 'industrial' AND area_ha > 2;

Save the result as a new layer. Everything below works on this shortlist.

3. Buffer the constraints

For each constraint layer, run Processing → Whitebox Toolbox → Vector → Buffer Vector:

• roads: a 100 m buffer (noise and access),
• protected areas: a 500 m buffer (legal setback).

Keep the buffers as separate layers; they become separate criteria.

4. Score each criterion

Turn each layer into a 0–10 score raster:

• Processing → Raster → Reclassify for rasters (for example, reclassify slope into suitability classes),
• Processing → Whitebox Toolbox → Raster → Conditional Evaluation for boolean layers (inside a buffer = 0, outside = 10).

Use the same 0–10 scale for every criterion so the final step is a fair average.

5. Combine into one surface

Run Processing → Whitebox Toolbox → Raster → Average Overlay with your score rasters as inputs. The output is a single suitability surface where high values satisfy the most criteria.

For unequal weighting, duplicate an important criterion raster before averaging, or use the raster calculator to apply explicit weights.

6. Extract and style the result

• Use Processing → Whitebox Toolbox → Raster → Corridor to connect the highest-scoring zones, or Clip Raster To Polygon to cut the surface to your study area.
• Style the surface with a colormap and drop the parcels on top to shortlist sites by eye.

Next steps

• Replace the average with Cost Distance when travel cost matters more than distance.
• Export the shortlisted sites with Export As HTML for stakeholders.