Measurements versus devices.

<p>Scatter plot of the number of measurements collected each day compared to the number of active devices at that day. The dark green symbols correspond to the most important spikes shown also in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081638#pone-0081638-g005" target="_blank">Figure 5</a>. The green and blue lines are guides for the eye and correspond to the case of one measure per device and two measures per device respectively.</p

Perception screen for WideNoise Plus mobile application.

<p>Perception screen for WideNoise Plus mobile application.</p

Estimation error.

<p>Difference between estimated and real dB value vs the number of measurements a user has performed.</p

Perception evaluation versus the measured noise level.

<p>The red lines display the average evaluation over the first five measurements of all users; the green lines correspond to the average evaluation over the set of all measures taken by users starting from the 50th one.</p

Estimated versus measured noise.

<p>Each point corresponds to one measurement, while both the colour scale light to dark grey and the point size represent the user expertise (small to large amount of previous measurements).</p

General space and time coverage.

<p>General space and time coverage.</p

Noise sample screen for WideNoise Plus mobile application.

<p>Noise sample screen for WideNoise Plus mobile application.</p

Distribution of measured noise levels.

<p>The plot shows the histogram of noise levels for the first measurements performed by users, compared to those performed after some experience is gained (after the 50th measurement).</p

Overall heatmap.

<p>Worldwide sample density, including all measurements, illustrated as a heatmap (© <i>OpenStreetMap contributors</i> for map data, used and redistributed under the CC-BY-SA licence<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081638#pone.0081638-OSM1" target="_blank">[26]</a>).</p

Tag screen for WideNoise Plus mobile application.

<p>Tag screen for WideNoise Plus mobile application.</p