Why Atlas totals are 2.3% higher than the official figures
Atlas measures polygons on the ellipsoid; the authors publish a "corrected area". The gap is a constant 2.3% in every country.
When Atlas compares its hectares with the national totals published with Global Mangrove Watch v4.1, every one of the 32 African countries is 2.3% higher in Atlas: the range is 2.3% to 2.3%.
What this tells us
- A constant ratio is not a country-specific mistake. If borders or labels were wrong we would see different percentages for different countries.
- The statistics file is named "corr_area", which indicates a corrected area statistic published by the authors. Atlas instead sums the geodesic area of the polygons (PostGIS
ST_Areaon the WGS 84 spheroid).
What it does not affect
- Shares and rankings (each country is scaled the same).
- Change between years (both are scaled the same).
What it may affect. If you compare an absolute number from Atlas with a number in the authors' tables, expect Atlas to be about 2.3% higher. For v3 maps the match is within 1%.
Recommendation. Quote the source of the area (Atlas measurement or official statistic) next to any number you publish.
Related reading
More in Methodologies
- How features are assigned to countries
- Provenance, checksums and the archive
- Carbon assumptions used in scenarios
- Diversity: Shannon index and evenness
- Field plots versus the map
- How carbon project locations are established and checked
- The official yearly series (1985–2025)
- Confidence labels: calculated, illustrative, assumed
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