# OSM data limits > Footprint coverage and estimated heights: how OpenStreetMap data quality affects the acoustic propagation and diffraction calculation, and when to trust it. Published: 2026-05-21 Category: acustica Tag: OpenStreetMap, Overpass API, Data quality, Acoustics Page: --- Two Open Lab tools — [Acoustic map](/en/tools/acoustic-map/) and [Barrier calculator](/en/tools/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](https://www.openstreetmap.org/): every contribution also improves the calculation of these tools. ## Tools that use this data - [Acoustic map](/en/tools/acoustic-map/) — ISO 9613-2 propagation with Maekawa diffraction on OSM buildings. - [Barrier calculator](/en/tools/barrier-calculator/) — Insertion Loss of a barrier, with OSM buildings as optional obstacles.