Trees per Citizen estimates the number of trees per inhabitant within a study area. It is a direct indicator of urban tree cover relative to the local population — higher values mean more trees available per person.
The KPI is calculated as the estimated tree count divided by the estimated resident population. It provides a concrete measure of urban green infrastructure and ecosystem services availability, including shade, air quality improvement, carbon sequestration, and thermal comfort. The UN-Habitat benchmark sets a minimum of 1 tree per 3 citizens (approximately 0.33 trees/person) as a threshold for adequate urban ecosystem services; more ambitious urban forestry targets call for 1 tree per citizen or more.
In densely built urban cores, the ratio often falls below 1 tree per person, while rural or peri-urban areas with forest cover can exceed hundreds of trees per inhabitant. This contrast makes the KPI a powerful diagnostic tool for comparing sites across the urban-rural gradient.
The KPI is computed by combining two independent spatial estimates: a tree count and a population estimate.
where the tree count is derived from a Tree Density Map at 10 m resolution (built from Sentinel-2 imagery and a canopy-counting algorithm), and the population is derived from the GHSL population grid at 100 m resolution (epoch 2020).
Data sources include ESA Sentinel-2 L2A imagery for tree detection and the Global Human Settlement Layer (GHSL) population grid (Pesaresi et al., 2024) for population estimates. The result is expressed as trees per person (dimensionless ratio).
Gauge. A semicircular gauge displaying the site's trees-per-citizen score and the control area value on a five-segment A–E quality arc.
Purpose: How does this site's tree cover per person compare to the surrounding control area, and what quality grade does it receive?
Description: The chart is titled "Trees per Citizen" with a topic badge "E4". Two nested gauges are displayed side by side: Site (left) and Control (right). Each gauge is a semicircular arc segmented into five colour bands (E to A, left to right). A white needle with a colour-filled circle indicates where the value falls on the arc. The extreme labels show "E / 0 trees" at the left end and "A / 5000 trees" at the right. Above the gauges, a grade badge shows the site's letter grade (A–E, colour-coded). A signed delta value (Site minus Control) indicates whether the site has more or fewer trees per citizen than the surrounding landscape.
150Trees per Citizen
How it's calculated: The site value is the trees-per-citizen score for the site polygon. The control value is the same metric computed for the control area (the reference landscape surrounding the site). The grade is assigned by the official thresholds: A > 2000, B 500–2000, C 100–500, D 10–100, E 0–10. The delta is the site value minus the control area value.
Note: This indicator is not inverted — higher values always indicate better ecological conditions.
Legend:
| Level | Range (trees/person) | Color | Meaning |
|---|---|---|---|
| A | > 2000 | ■ #00A67A | Excellent — strongly forested, abundant tree cover |
| B | 500–2000 | ■ #00DF80 | Good — peri-urban or small town, widespread trees |
| C | 100–500 | ■ #FFD21E | Moderate — urban periphery with parks or corridors |
| D | 10–100 | ■ #FF8B16 | Poor — suburban, insufficient public green |
| E | 0–10 | ■ #FF367F | Critical — dense urban/industrial, very scarce trees |
Interpretation example:
If the gauge shows grade E and a site score of 0.0 trees/person, it means the site has essentially no tree cover relative to its resident population — typical of a dense urban or industrial zone with no significant green areas and very high biodiversity risk.
Highlights Table Row. A row in the KPI comparison table on the Overview page showing the site's trees-per-citizen value alongside other key environmental KPIs.
Purpose: How does this site's tree cover per person rank relative to other monitored sites at a glance?
Description: The Highlights table lists multiple KPIs in rows. The "Trees per Citizen" row displays the latest trees-per-citizen value with contextual colour-coding and a grade badge, alongside the control area value. This allows high-level cross-KPI comparison on a single screen.
How it's calculated: Same formula as the Assessment gauge. The value shown is the site's current trees-per-citizen ratio. The grade is assigned by the same A–E thresholds.
Interpretation example:
If the Trees per Citizen row shows 0.0 highlighted in red (grade E), it signals that this site has essentially no trees relative to its population — a flag for urgent green infrastructure intervention.
Data Table. A column in the multi-site comparison table listing trees-per-citizen values for both the site and its control area across all monitored sites.
Purpose: How does the tree cover per person at each monitored site compare to its control area, in a tabular view covering all sites?
Description: The comparison table includes a column labelled "Trees per Citizen (Site/Control)". Each cell shows the site value and the control area value side by side. The table can be copied as CSV for external analysis.
How it's calculated: The site and control area trees-per-citizen values are computed with the same formula (tree count divided by population) and displayed in the same cell. Values are rounded to one decimal place.
Interpretation example:
If a site shows 0.0 / 1.8, it means the site has 0 trees per citizen while its control area has 1.8 — the site is severely below the surrounding landscape and below the UN-Habitat minimum threshold.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| GHSL Population Grid (GHS_POP R2023A) | JRC / EU | Global | 100 m | 2020 |
| ESA WorldCover | ESA | Global | 10 m | 2021 |
| Impact Observatory Annual LULC | Impact Observatory | Global | 10 m | Continuous |
| Google Dynamic World | Global | 10 m | Continuous | |
| ESA Sentinel-2 L2A | ESA / Copernicus | Global | 10 m | Continuous |
The tree count is derived from a Tree Density Map at 10 m resolution, built from Sentinel-2 imagery (NIR, Red-Edge, and SWIR bands) using a canopy-counting algorithm trained on reference samples. Post-processing with Land Cover data (NAA map, ESA WorldCover, Google Dynamic World) excludes non-vegetated areas. The pipeline counts tree canopy crowns within the site polygon boundary.
Population is derived from the GHSL (Global Human Settlement Layer, Pesaresi et al., 2024) population grid at 100 m resolution, epoch 2020. The total population within the site polygon is obtained by spatial integration of the population density raster.
The full processing pipeline:
The result is expressed as trees per person (dimensionless ratio). A new version is generated per CLC land cover version, on demand.