About the calculation
How we work out the sun
We work out how many hours of direct sun reach the facade and the floor you choose — not just which way the wall faces. The basis is public elevation and building data from Kartverket, the Norwegian mapping authority, and from Matrikkelen, the national property register.
Every address is worked out the same way
The same method runs for every address, built on the same public elevation and building data. No manual adjustment and no guesswork per home — which is what makes the figures comparable from one address to the next.
More than which way the wall faces
Most property listings say which direction a facade faces. That says nothing about whether the building next door or the trees actually let the sun through. We work out whether the sun gets past what stands in the way — buildings, vegetation and terrain — not just the compass direction.
The sources
Elevation data: © Kartverket's laser scan, flown 18 May 2024 (CC BY 4.0 / NLOD). Building data: © Matrikkelen, the public register of buildings and addresses (NLOD). Building outlines: © OpenStreetMap contributors (ODbL).
Calculation version
Every report is stamped with a calculation version and the date the source data was scanned. Together they say which calculation the figures came from, so two reports for the same home can be compared even if they were retrieved months apart.
We change the version when an improvement to the calculation can move a figure on the report — not when we change the look or the wording. So if a figure moves between two versions, it is the calculation that has got better, not the home that has changed. A downloaded PNG or PDF carries the same stamp, so a saved answer can always be traced back to the calculation that made it.
Checked against the physics, not against the ground truth outside
The position of the sun is checked against known astronomy: the calculated solar elevation and direction match the reference values for Oslo at the solstices and the equinoxes.
The shadows have no ground truth to be measured against. The figures have not been compared with other sun tools or with shadows photographed on site, and they are not going to be — we dropped that plan rather than point at a check nobody was going to run.
What remains is a set of requirements the machine re-checks for every single building: the sun cannot, for instance, get smaller the higher up the floors you go. Break one of them and the calculation stops. That does not catch an error in the method itself, and we say so plainly rather than calling it quality assurance.
December is a minimum figure
The laser scan was flown in May, with leaves on the trees, and the elevation data cannot tell us whether a tree is deciduous or a spruce. December is therefore worked out as if the leaves stayed on all winter. The figure you get is a minimum: if a deciduous tree is in the way, the home gets more sun in December than the figure promises — never less.
If there is foliage between the sun and the wall, the report also shows what gets through once the leaves are gone, and December stands as a range from the minimum figure upwards. If no foliage is in the way, there is nothing to get through, and the two ends land on the same figure. That is an honest limit, not an excuse.