The data includes current built green roofs, spontaneously created green roofs, and potential green roofs in the Helsinki metropolitan area.
The material was produced by first identifying the buildings with more than 10% of flat (less than 12 degrees) roof if the roof area is under 100 m2, or 5% if the roof area is over 100 m2. Next, those flat roofs with more than 10% vegetation of the suitable area were identified based on the 2013 regional false-colour orthophoto. The method of identifying green roofs has been intentionally set to be slightly hypersensitive, so that no green roofs are accidentally overlooked. After this, the roofs automatically identified as green roofs were visually reviewed and, if necessary, moved to the category of either spontaneous or potential green roofs.
Potential green roofs include roofs with sufficient flat surface area, but where no vegetation was detected. The attribute data for potential green roofs includes VAIKUTUS (impact), which indicates how much impermeable area there is around the building in question, within a radius of 100 metres. The range of the figure is 0 (permeable surroundings)...1 (completely impermeable surroundings).
The material was produced in the Decumanus project by the German Aerospace Center (DLR).