The 30: at least 30% tree canopy where you live

How much of the land around a home lies under a tree crown? For every residential building we measured that within 500 m of its facade, on a map of 25 by 25 cm cells from 2024. A neighbourhood, district or municipality then adds up its homes.

Zuid-Holland, technische totaalkaart 2024, homes BAG 2026, neighbourhoods CBS 2025.

What is measured?

The paper asks for at least 30% canopy cover in every neighbourhood, and stresses that it is about the neighbourhood, not the average of the city. We take as the neighbourhood of a home everything within 500 m of its facade, and calculate:

canopy cover = area under tree crowns ÷ land area × 100%, within 500 m of the facade

On the map every building has its own colour. An area shows the share of homes that reach 30%; the mean canopy cover of those homes is in the popup.

What the result assumes

The paper leaves open from where and how far to measure. The choices below fill that in and make the most difference to the figures. Where a choice pushes the result one way, it says so; the reasons are under "Choices and why".

• 500 m from the facade. The zone runs around the whole footprint of the building, so a large building gets a larger zone than a terraced house. With a smaller radius more homes would reach 30%, because the street and the garden would weigh more.
• Across boundaries. The zone does not stop at the boundary of the neighbourhood, the municipality or the province. A home at the edge of a wood counts that wood, also when it lies in the next municipality.
• Divided by land area. Water and bridges over water do not count. A home on a lake is not marked down for the water. (more favourable)
• An area is the sum of its homes. A block of 100 flats counts 100 times, a detached house once. The share says how many people reach the 30, not how much ground.
• Street and garden trees count. The crown map is made from lidar; what exactly counts as a crown is up to that map.

Steps

1. Where are crowns? Friedenau Society's technische totaalkaart 2024 divides the whole of the Netherlands into cells of 25 by 25 cm. For each cell it gives what is there (water, grass, farmland, paving, shrubs, building, bridge) and whether a tree crown hangs over it. The crowns are those of the Boomkroonbedekking 2024 (BKB 2024). The map is made from lidar: laser height measurements from an aircraft.
2. Where is land? Everything except water, bridges over water and land abroad is land. A crown over water or over a bridge does not count.
3. Adding up per 5 m. For every 5 by 5 m square (400 cells of 25 cm) we counted how many cells are land and how many of those lie under a crown. That makes the calculation per home fast, while the result hardly changes.
4. The zone of each building. Around every residential building from the BAG (the same buildings as for the 3), a zone of 500 m from the facade was drawn. Within that zone crown and land were added up: crown ÷ land × 100%. Checked on 45 buildings in Delft, the difference from an exact calculation is at most 0.03 percentage points.
5. Neighbourhoods, districts and municipalities. Every building belongs to the neighbourhood that holds its centre, and so to a district and a municipality, as for the 3. Per area: the share of homes with at least 30%, and their mean.

Choices and why

There are trees near my home: why this colour?

A few trees in the street or the garden usually do not reach the 30. A zone of 500 m from the facade is at least 78 hectares: 30% of it is about 24 hectares under crowns, more than 30 football pitches. Mostly homes at or in a wood, a large park or an estate reach that. Half of the buildings in Zuid-Holland are below 11%.

Per home this is an indication from a map, not a measurement on site. Trees planted or felled after 2024 are not in it yet.

Compared with the 30 per neighbourhood

Until 19 October 2026 the map showed the canopy cover of each CBS neighbourhood itself: the area under crowns in the neighbourhood divided by its land area. By that calculation 8.1% of the land in Zuid-Holland lies under a crown and 102 of the 2,509 neighbourhoods reach 30%. Per home the mean comes out higher (12.7%), probably because homes stand near trees more often than near meadows and greenhouses, which take up much of the area in the neighbourhood figures.

Before that, the 30 came from a calculation with the crown polygons of the NEO trees (2020–2022) on the CBS neighbourhoods of 2023. It gave higher values throughout, usually about 23% higher, mainly because a crown on a neighbourhood boundary counted in full in each neighbourhood and overlapping crowns were added up.

Limitations

• What a crown is is up to Friedenau Society's map. Very small trees and shrubs may or may not be in it, depending on how that map was made.
• Squares of 5 m. A square counts when its centre lies in the zone. At the edge of a 500 m zone that is a few metres at most.

Code and sources