1. Sources
- Aerial image: SWISSIMAGE by swisstopo. The dossier states the flight year of the evaluated image.
- Official cadastral survey: land cover and buildings of the canton, obtained via geodienste.ch. The dossier states the data status.
Information from the official cadastral survey without warranty and without legal effect.
Bauland-Scout currently covers 18 cantons. In the other eight cantons (LU, OW, NW, SG, VS, VD, NE, JU), the required geodata are currently not openly available for this use, or clarification is still under way. Further cantons will follow as soon as the data allow.
2. Two levels
Aerial image checked: nothing noticeable: the aerial image shows no building and no installation on the plot (except small structures under 12 m²), and the official cadastral survey records no building of 12 m² or more there.
Aerial image checked: to be clarified on site: no building was detected on the aerial image, but at least one circumstance calls for clarification on site. The dossier lists each reason separately.
Examples of reasons for the level “Aerial image checked: to be clarified on site”:
- use as a garden, for example allotment gardens
- paved area
- shelter of 12 m² or more
- planned building
- plot under 500 m²
If a source is missing or the data of the official cadastral survey are older than 180 days, no note appears.
3. Notes
In addition to the level, the dossier lists these notes:
- small structure under 12 m², visible or recorded
- part of the area is recorded as forest or wooded
- a body of water touches the area
Trees and shrubs do not lead to the level “Aerial image checked: to be clarified on site”.
4. Limits
- The aerial image shows the state at the time of the flight; later changes are not visible.
- The evaluation is not a certified extract. Official information is provided by the competent surveying office.
- It replaces neither a site visit nor information from the building authority.
- Undeveloped does not mean that a plot is for sale.
5. How reliable is the note?
In two randomly drawn samples of 150 plots each with the note “Aerial image checked: nothing noticeable”, separate image evaluations supported the finding in 86 to 87 % of cases when cases in which they disagreed are strictly counted as not confirmed. With a third check based on an image of the surroundings and the plan, it was 94 to 95 % (as of 04.11.2026).
The first sample was measured against the previous version of the checking rule, the second against the current one.
The note is therefore an indicative value: the situation on site may differ. It does not replace a site visit or information from the building authority.
6. Small structures in the building register
If the Federal Register of Buildings and Dwellings lists only small structures under 20 m² on a plot (for example a garden shed or storage shed), the plot appears with “Clarification needed” and an explicit note in the dossier. This applies only to infill plots with an established building area; entries in the building classes industry, religious buildings and sport remain excluded.
The basis is a random sample of 150 such plots (as of 09.11.2026). For the infill plots, no larger building was visible on the aerial image in 61 of 64 cases: 95.3 % (95 % range 87.1 to 98.4 %). Across all 150 plots it was 84.7 % (78.0 to 89.6 %), which is why only the subgroup of infill plots is included.
Caveats: the subgroup was chosen after the draw, each image was assessed once by automated analysis, and many of these plots are gardens or allotments. Plots of 500 m² or more are also checked on the aerial image in the regular process: if it shows a larger building, the plot is excluded again. Smaller plots do not receive this aerial check.