Two Open Lab tools — Acoustic map and Barrier calculator — use OpenStreetMap buildings as obstacles for propagation and diffraction calculations. OSM buildings are, however, data of uneven quality: this article explains the two main limitations, their effect on the calculation, and when the result is reliable.
Why our tools use OSM
Buildings are obstacles that attenuate and diffract sound: ignoring them overestimates levels downwind of a structure. OpenStreetMap is today the only global source of building footprints that is open and queryable live — through the Overpass API — with no paid licence: the natural choice for a demonstrative tool that runs entirely in the browser. The price of this openness is that the data is produced by volunteers, with quality that varies widely from place to place.
Two levels of problem
Footprint coverage
In Italy there is no cadastre import into OSM: the licence of cadastral data is not compatible with OpenStreetMap’s ODbL licence. (The catasto is the Italian land registry, the official source of building geometry.) Buildings are therefore hand-drawn by mappers, typically tracing AGEA orthophotos — open-licence aerial imagery from the Italian agricultural agency. The result is uneven coverage: city centres are often well mapped, while suburbs, industrial zones and rural areas are only partly covered. A building that is not mapped does not exist for the calculation.
Heights
Even when the footprint exists, the height is often missing. The height and building:levels tags are present on only a minority of buildings. When they are absent, the tools apply a default height (9 m, roughly three storeys). In areas like Treviso the large majority of buildings fall into this category: the height used in the calculation is an estimate, not a measurement. The Building data quality card in the tool panel shows in real time how many buildings have a real height and how many an estimated one.
Effect on the calculation
- Missing building — the obstacle is not seen, screening attenuation is underestimated and the level at the receiver comes out higher than reality.
- Estimated height — knife-edge diffraction (Maekawa) depends directly on the edge height: a wrong height shifts the computed attenuation.
- Typical error — on the order of ±3–5 dB at a single receiver in unfavourable geometry. Enough to change the outcome of a compliance check.
When the calculation is reliable
- Well-mapped city centres: visually check on the map that all the relevant buildings are present.
- Short source-to-receiver distances, where the effect of buildings is secondary to geometric spreading.
- Scenario comparison: the delta between two configurations (with and without a barrier) is more robust than the absolute value, because the systematic errors of the buildings partly cancel out.
When it is NOT
- Poorly mapped suburbs and industrial zones: check the percentage of estimated heights in the panel card.
- Geometries dominated by a few critical buildings, where a single wrong value weighs heavily.
- Design decisions or compliance checks: here a field survey or a dataset with real heights is needed.
Future alternatives
- Regional DBT datasets — the DataBase Topografico of Veneto, Lombardy and other Italian regions (a regional, cadastral-grade topographic database) describes buildings with real eave and base elevations, derived from official cartography. A “DBT” mode is on the tools’ roadmap.
- Microsoft Building Footprints / Overture Maps — extensive global coverage, generated via machine learning on satellite imagery, under an ODbL-compatible licence: useful above all to fill coverage gaps.
How to report a missing building
OpenStreetMap can be edited by anyone. If you spot a building that is absent or has no height in the area you care about, you can add or correct it on openstreetmap.org: every contribution also improves the calculation of these tools.
Tools that use this data
- Acoustic map — ISO 9613-2 propagation with Maekawa diffraction on OSM buildings.
- Barrier calculator — Insertion Loss of a barrier, with OSM buildings as optional obstacles.