Mapping Toronto’s Green Spaces with Sentinel-2 NDVI

Toronto is known for its vibrant urban forest, from High Park and the Don Valley to the quiet corridors of neighborhood parks. But how green is the city really? To answer this, I used Sentinel-2 multispectral imagery and Normalized Difference Vegetation Index (NDVI) analysis to map vegetation health across Toronto’s urban green spaces.

What Is NDVI?

NDVI is one of the most widely used vegetation indices in remote sensing. It leverages the difference between near-infrared (NIR) and red reflectance to quantify plant vigor:

Healthy vegetation reflects strongly in the NIR band and absorbs visible red light, producing NDVI values close to 1.0. Low or negative NDVI values indicate sparse vegetation, bare soil, or built-up areas.

Data and Workflow

The analysis was conducted using Google Earth Engine (GEE) and OpenStreetMap (OSM) green space boundaries:

1. AOI: City of Toronto and surrounding GTA municipalities.

2. Imagery: Sentinel-2 Level-2A (surface reflectance).

3. Date Range: Summer 2024 (June–August) to minimize cloud and seasonal variation.

4. Processing Steps:

   • Cloud and shadow masking via SCL band.

   • NDVI computation from NIR (B8) and RED (B4) bands.

   • Mean NDVI extraction over OSM park polygons.

   • Visualization using a dark basemap for contrast.

     
     

The resulting map (shown below) highlights Toronto’s urban ecological backbone such as river valleys, golf courses, and major parks glowing in bright green tones that represent high NDVI.

Insights

• Don Valley and Rouge Park stand out with consistently high NDVI (0.7–0.9), indicating dense, healthy canopy cover.

• Downtown and waterfront areas show patchy greens with moderate NDVI (~0.4–0.6), consistent with mixed lawns, shrubs, and street trees.

• Suburban corridors connecting Vaughan, Markham, and Pickering reveal continuous green belts, which is essential for biodiversity and urban cooling.

  
  

This analysis confirms that Toronto’s urban forest is not just decorative but rather it forms an interconnected ecological network supporting air quality, carbon storage, and mental wellbeing.

Why It Matters

NDVI-based mapping allows city planners, ecologists, and citizens to:

• Track vegetation change over time,

• Identify stress zones from drought or development, and

• Quantify the environmental benefits of green infrastructure.

  
  

As climate change intensifies, continuous monitoring of vegetation health in urban areas will be key to maintaining sustainable, livable cities.

Tools and Code

The workflow was built using:

• Google Earth Engine JavaScript API

• Folium and Leafmap for visualization

• OpenStreetMap for green space geometries

  
  

Toronto’s green heartbeat is visible from space where NDVI helps us measure how strongly it beats.