Canopy index

**Definition** The canopy corresponds to the upper floor of the trees: it is the set of leafy crowns or crowns of all trees in a territory. Thus, the canopy index of a city represents the percentage of the area occupied by that canopy in relation to the total area of the city. To calculate it, it is necessary to define a height above which all the spaces occupied by the trees are taken into account: most metropolises (and this is the case of Paris) have chosen the height of 3 metres, which makes it possible to take into account all trees of small, medium and large development. **General principles for calculating canopy index** To calculate the canopy index, it is necessary to have as accurate a mapping as possible of all vegetation above 3m in the territory of the municipality. To carry out this mapping, two types of information are needed: * A map layer to identify all the points where there is vegetation. This detection is made using infrared data: chlorophyll – present mainly in the leaves – absorbs the red part of the light spectrum, which makes it possible to identify vegetation. * A map layer to identify the height of all points in the territory and thus extract points above 3 metres. These heights can be calculated either by LIDAR shots (a type of radar on board during aerial shots) or by directly using digital height models transmitted by the National Institute for Geographical and Forestry Information (IGN) or the National Center for Space Studies (CNES). The combination of these two layers thus makes it possible to obtain a map of all the vegetation points located at a height of more than 3 metres.