The Sossego Index methodology, step by step.
For every search we load from OpenStreetMap everything that produces noise within a few kilometers: roads classified from motorway to residential street, railways and surface metro lines, airport runways within 15 km, industrial zones, stadiums, bars, pubs, nightclubs and bus terminals.
Each road type gets a reference emission level at 10 meters, in dB(A), based on typical values from the traffic noise literature: motorways around 78, arterial roads 73, collectors 68, local streets 61, residential streets 48. Extra lanes and high speed limits raise the value; 30 km/h zones lower it.
Railways count as 70 dB(A) line sources. Airport runways count as long-range sources in three sizes: international, regional and small. Bars and nightclubs count as short-range point sources.
Roads, railways and runways are treated as finite line sources. The level drops about 3 dB every time the distance doubles, corrected by the angle the segment subtends from the point, which avoids counting split segments twice. Point sources drop 6 dB per doubling of distance. We also add an attenuation for air and ground absorption, about 1.8 dB per 100 meters for roads.
All contributions are summed in energy, not in dB, and combined with an urban noise floor of 38 dB(A). The result is the estimated noise at the point.
People who live in an apartment can enter the floor and the direction their windows face. The receiver height is the floor times 3 meters, and the distance to every road, railway and local source becomes the slant distance: a motorway 18 meters away, seen from the 10th floor, is 35 meters away, about 3 dB less. Ground attenuation shrinks with height, down to 60% of the street value around the 10th floor, because high floors hear distant noise better over the rooftops.
The facing uses the angle between the window direction and each source. Sources within 60° of the window direction count in full; to the side, up to 120°, they lose 3 dB; behind the building they lose 12 dB, the typical difference between an exposed and a shielded facade. Airports do not change with floor or facing: the sound comes from above. The heatmap still shows the street level.
The index maps the estimated noise onto a 0 to 100 scale. 48 dB(A) or less scores 100; 86 dB(A) or more scores 0. In between the relation is linear, about 2.6 points per decibel.
The Brazilian standard ABNT NBR 10151 defines reference levels for assessing noise in inhabited areas. For mixed, predominantly residential areas the value is 55 dB(A) during the day and 50 dB(A) at night; for commercial areas, 60 and 55 dB(A). A Calm point on the index sits near the daytime residential limit; Very calm sits below it.
The model ignores buildings, walls and terrain, which can reduce noise by tens of decibels. We do not use real traffic counts or time of day, so the value represents a typical day. OpenStreetMap coverage varies between cities. Treat the number as a first approximation, not as a report.