Data and accuracy
What Shadeline calculates exactly, what it estimates, and where the map can be wrong.
Sources
| Source | Used for | Terms |
|---|---|---|
| OpenStreetMap | Buildings, their heights, land cover | Open Database License |
| OpenMapTiles, OpenFreeMap | Vector tile schema and hosting | Open |
| Mapzen Terrain Tiles | Elevation of the ground | Open data |
| NASA POWER | Monthly solar climate averages | Public |
| NREL Solar Position Algorithm | Position of the sun | Published algorithm |
How the figures are made
- Sun position
- The position of the sun comes from the NREL Solar Position Algorithm, and our implementation is checked against the pvlib reference. Sunrise and sunset include atmospheric refraction.
- Shadows
- Each building is raised from its OpenStreetMap footprint to its mapped height. The ground comes from elevation tiles. Both cast shadows on each other.
- Sun-hours map
- For every cell of the area the sun is sampled every 10 minutes between sunrise and sunset, and a ray is traced towards it. The map shows the hours in which the ray reaches the sun.
- Point report
- Direct sun on the chosen day is sampled every 5 minutes. The sky view factor is the share of the sky that is visible from the point, measured in several hundred directions.
- Yearly energy
- Annual irradiation combines a clear-sky model with monthly climate averages from NASA POWER, so typical cloudiness is included, and applies the shading found at the point. When climate data cannot be loaded, the clear-sky figure is shown and labelled as such.
Limits
- Building heights can be missing or out of date. A building without a height is drawn at a default height and marked as estimated.
- Roofs are flat. Pitched roofs, balconies and facade details are not modelled.
- Trees are illustrative stand-ins in wooded areas. Individual trees are not on the map.
- New construction appears only after it has been mapped in OpenStreetMap.
- Yearly figures use climate averages, not the weather of a particular year.
- Results are estimates. Do not rely on Shadeline alone for construction, legal, financial or safety decisions.
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