Photographic comparison: a method for qualitative outdoor thermal perception surveys

This article addresses the use of photographic comparison as a complementary visual appraisal method in an outdoor thermal perception survey. This survey was carried out during a Ph.D. research exploring how materials and vegetation influence thermal comfort in outdoor public spaces. Objective and subjective thermal perception parameters were combined and quantitative and qualitative research methods were used. The quantitative methods included microclimatic measurements, whilst the qualitative methods comprised observations and spatially localised interviews based on a questionnaire and the photographic comparison. This article explores how such visual research method allowed triangulating findings of this field survey. Three non-edited photographs of outdoor public spaces, under similar summer meteorological conditions but with contrasting spatial features, were shown to respondents to the questionnaire. The photographs depicted undisclosed locations for preventing biased emotional appreciations. Respondents were asked to select the potentially most comfortable and uncomfortable environments depicted. The choice of photographs matched the previous answers on the thermal sensation and evaluation judgement scales. Hence, we discuss the way the visual interpretations by respondents allowed the triangulation of in situ thermal perception data. The extent to which thermal comfort can be interpreted from thermal environments depicted in photographs containing clear visual signs is further discussed. The article concludes on how such a visual appraisal method can be valuable for enriching future qualitative outdoor thermal perception surveys with subjective interpretation of visual data.