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Creating a Custom Area of Interest (AOI)

This guide explains how to create your own Area of Interest (AOI) for the Deforestation Viewer, allowing you to analyze NDVI change over any chosen region.

1. Install QGIS

Download and install QGIS 3.x from the official website:

https://qgis.org

During installation: - Accept default options. - Ensure GDAL support is installed (included in recent QGIS versions).

Once installed, launch QGIS. You should see an empty map canvas.

2. Add a Basemap

QGIS opens with a blank grid by default. To add a satellite basemap, install the QuickMapServices plugin.

Install QuickMapServices

  1. In the menu bar, go to Plugins → Manage and Install Plugins…
  2. Search for QuickMapServices and click Install Plugin.

Add a Basemap

  1. Go to Web → QuickMapServices → Settings
  2. Click More Services → Get Contributed Pack → OK
  3. Then open Web → QuickMapServices → ESRI → ESRI Satellite

You should now see high-resolution satellite imagery.
This provides a visual reference for accurately drawing your AOI.

3. Draw Your AOI

  1. In the Layers panel, select New Shapefile Layer → Polygon
    (or use Layer → Create Layer → New GeoPackage Layer if preferred)

Creating new polygon layer in QGIS

  1. Set CRS to EPSG:4326 (WGS 84)
  2. Click OK to create the layer

  3. Right-click the new layer → Toggle Editing

    Toggling editing in QGIS

  4. Use the Add Polygon Feature tool to draw your AOI (e.g., a forest, park, or region of interest)

    Adding polygon feature

  5. When done, right-click → Save Edits, then toggle editing off

Tip:
Start with a relatively small AOI (a few thousand km² or less) when testing.
Larger AOIs may take significantly longer to process.

4. Export to GeoJSON

The viewer expects your AOI to be stored as a GeoJSON file at:

data/aoi/roi.geojson

To export:

  1. Right-click your AOI layer → Export → Save Features As…
  2. Set:
  3. Format: GeoJSON
  4. CRS: EPSG:4326 – WGS 84
  5. File name: data/aoi/roi.geojson
  6. Click OK

Save AOI Layer Choose polygon type

Your project directory should now look like:

deforestation-viewer/
├── data/
│   └── aoi/
│       └── roi.geojson

5. Verify the AOI

Option A — QGIS

Re-open the saved GeoJSON file in QGIS to ensure it displays correctly and covers the intended region.

Option B — Python

Verify the AOI programmatically:

import geopandas as gpd

gdf = gpd.read_file("data/aoi/roi.geojson")
print(gdf.crs, gdf.total_bounds)

Expected output: 

EPSG:4326 and valid longitude/latitude bounds

If CRS or coordinates appear incorrect, re-export the file with the correct settings.

6. Troubleshooting

Issue Likely Cause Fix
AOI not showing or blank Wrong CRS Reproject to EPSG:4326 before export
AOI appears offset or distorted Latitude/longitude order flipped Ensure GeoJSON uses longitude first
Processing fails or hangs AOI too large Use a smaller AOI for testing
No imagery found AOI outside Landsat/Sentinel coverage Choose a region with global satellite data availability

7. Next Steps

Once your AOI is saved and verified, you can: - Run the NDVI processing pipeline (search_download.py) to generate annual composites
- Visualize NDVI and vegetation change in the Streamlit app (streamlit_app.py)

For detailed instructions, see: - NDVI Composite Builder - Streamlit Viewer Guide