Mahajanga vs Nacala
Tree cover and air quality for both, measured the same way: Sentinel-2 imagery at 10 m detail over a 2 km radius from each city centre, and the live US EPA air quality index. Same radius and same index, so the two numbers compare directly.
Mahajanga has more tree cover — 7.0% against 2.3%.
Mahajanga has cleaner air right now — AQI 27 against 28.
- Tree cover gap
- 4.7 points
- Mahajanga is ahead.
- Air quality gap
- 1 AQI
- Mahajanga is cleaner.
- Trees between them
- 9.5K
- Mahajanga has more standing.
Tree cover
Share of the 2 km radius under canopy.
7.0%
2.3%
Air quality index
US EPA index, live, with its band. Lower is better.
27 · Good
28 · Good
Trees standing
Estimated from the measured canopy area.
16.6K
7.1K
Trees still needed
To reach the same canopy target. Fewer is better.
54.6K
85.4K
CO₂ absorbed each year
By the trees already standing.
366K kg
156K kg
Air quality in detail
What each city is breathing
Concentrations in µg/m³, measured at the same moment as the index above. Lower is better in every row. Both are modelled, with no ground station close enough to either.
PM2.5
Fine particles, the pollutant that usually sets the index.
6.4 µg/m³
6.7 µg/m³
PM10
Coarser particles — dust, pollen, road grit.
10.9 µg/m³
10.3 µg/m³
Nitrogen dioxide
Mostly traffic and combustion.
0.6 µg/m³
0.1 µg/m³
Ozone
Forms in sunlight; peaks on hot, still afternoons.
64 µg/m³
57 µg/m³
The last week, day by day
A single reading can catch a city on a bad afternoon. The week says whether it was the weather or the place.
| Day | Mahajanga | Nacala |
|---|---|---|
| 22 Sept | 28 | 38 |
| 23 Sept | 30 | 39 |
| 24 Sept | 40 | 31 |
| 25 Sept | 30 | 35 |
| 26 Sept | 30 | 42 |
| 27 Sept | 34 | 42 |
| 28 Sept | 25 | 25 |
Reading these numbers
What is actually being measured
Tree cover
The share of ground under canopy inside a 2 km radius of each city centre, read from Sentinel-2 satellite imagery at 10 m detail. It is a measurement of that circle, not of the whole municipality — which is exactly what makes the two comparable, since city boundaries are drawn to wildly different rules around the world. Mahajanga leads here at 7.0%.
Air quality index
The live US EPA index, computed from current pollutant concentrations — ground stations where a city has them nearby, and a model everywhere else. It moves hour to hour, so this is a snapshot rather than a verdict on either place: Mahajanga reads 27 (good) and Nacala reads 28 (good) right now.
Frequently asked
Mahajanga and Nacala, answered
Which has more trees, Mahajanga or Nacala?
Mahajanga, with roughly 16,625 trees inside its 2 km radius against 7,088. Tree cover tells a slightly different story from raw count: Mahajanga has the denser canopy at 7.0%.
Which has better air quality, Mahajanga or Nacala?
Mahajanga right now, at AQI 27 against 28 — a gap of 1 points. This is a live reading rather than an annual average, so it can reverse within a day.
How many more trees does each city need?
Mahajanga needs about 54,626 more to reach its canopy target, and Nacala about 85,369. The target is the same share of ground for both, so the figures are directly comparable.
Are these two measured the same way?
Yes — that is the point of the page. Identical radius, identical satellite source at 10 m detail, and the same US EPA index for air. Nothing here is adjusted for population, city limits or climate, so the numbers describe the same-sized circle of ground in each place.
Keep going
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