Visualizing Noise – An Outline of Experiences and Challenges
In Europe maps are used to tackle the problem of urban noise. Noise is “amongst the most relevant environment and health problems, just behind the impact of air quality” (European Commission, 2014). Noise maps have to be drawn up every five years according a directive by the European Union and are used to monitor noise and to inform and consult the public about noise exposure. Therefore they are a vital part of public discussion and exemplify how maps are used for public participation and how decisions in environmental planning are made by the means of maps. However, discussions and decisions also depend on users’ interpretation of the presented content. In case of noise maps a variety of aspects have an effect, e. g.: • The choice of the presented content: The EU directive defines the noise indicator Lden to be presented. This is the A-weighted long-term average sound level for individual noise sources, such as traffic, airport noise, and railway noise. This indicator is only one way of presenting noise, other indicators can lead to different values and thus visual appearances, which is misleading for non-expert users as all indicators represent the noise pressure level in the unit dB. • The visual variables: Usually equal-noise contours are presented by means of different colors, but as colors are connotative and color interpretation depends on subjective perception the choice of color effects map interpretation. Also the size of an area has shown an influence on the interpretation of noise pollution: bigger areas, such as wider roads, have been interpreted as more polluted although they showed the same dB-values as narrow roads. • The spatial positioning of graphical variables which represent measured or modelled values in connection with background knowledge: Results of a study suggest that participants assessed measurements near a road higher than measurements taken further away. Thus, they did not only interpret maps on basis of the information presented by means of graphical variables, but by combining background knowledge - it is louder nearby a road - with the position of the displayed value. However, in case of noise, background knowledge can be naïve because the calculation of the dB-values is complex, especially because of the logarithmic scale. This contribution’s aim is to outline the results of empirical research dealing with the cartographic design of noise maps that are in line with the European Noise Directive. Therefore we will present principle findings of four user studies which were undertaken during the iterative design process of a color scheme for the presentation of noise immission in maps as well as insights gained in a requirements analysis and an interview with people affected of noise of the airport London Heathrow. From these findings we will derive major challenges for the visualization of noise in general and by doing so we will outline an innovative research perspective. General principles can be translated to other sorts of environmental information with similar characteristics as sound.