How we calculate

Updated August 22, 2026

Every number on this site can be traced to a formula and a source. This page is that trace.

Geometry

Areas and perimeters are computed on the drawn polygon with the shoelace formula in a local metric projection (metres). The cadastre delivers parcels in WGS84; we project them before measuring, so the area matches the official figure within rounding. All areas are planimetric, like deeds and the cadastre.

Slope

Slope is rise ÷ run. From coordinates we read elevation at a grid of points across the plot through Open-Elevation (SRTM 30 m and national DEMs where available). Error margin: the elevation model itself is ±5–10 m absolute but far better relative; over a 30 m cell the slope is an average, not a survey. Steps, walls and terraces are invisible to it. Use it to orient, not to design.

Sun

Sun position uses the SunCalc implementation of the NOAA solar position algorithms for the plot centroid, date and time. Shadows in the 3D view are cast by the volumes you place at their declared height; terrain shading is not modelled yet.

Costs

Cost figures are ranges from public statistics and industry surveys, shown with source and verification date next to each table. They are national or regional averages: your quote will differ. Currency and units follow the market (USD · imperial for en-US; EUR · metric for es-ES).

Regulation

Setbacks, coverage and minimum lot sizes vary by municipality. Where we show a value it is a typical or default one, clearly labelled; always check the local plan.

Update frequency

Constants are reviewed at least every six months and when a source changes; the date next to each figure says when it was last checked. Content that loses relevance is refreshed or withdrawn.

Report an error

Use the contact form with the reason "Report a data error" and the URL. Corrections are published with the new verification date.