Can you really see 'green'? Assessing physical and self-reported measurements of urban greenery

Urban vegetation provides a wide array of services; yet, there is still a knowledge gap regarding the mechanistic processes behind urban vegetation-human well-being relationships. Two main approaches have been used to assess urban greenery associated with human well-being: physical and self-reported. We here assessed the associations between physical (green view index-GVI, green cover-GC) and self-reported measures (perceived visible greenery-PVG) of the streetscape greenery of two southeastern Mexican settlements (Xalapa, Coatepec). Our results show that both sites have considerable GC (Xalapa = 37.2%, Coatepec = 47.4%). We found a clear association between GVI and GC in Xalapa, but none in Coatepec. The latter was due to an important proportion of the vegetation of Coatepec being mainly constrained at block interiors, obstructed by walls. Regarding the self-reported measure, our results show an important discrepancy in relation to one of the physical measures (GVI), assessed through PVG/GVI ratios. In general, respondents tended to overestimate greenery, with greater overestimations related to GVI values < 10%. Among the assessed respondent traits (gender, education level, live and/or work in neighborhood, time living and/or working in neighborhood), we found none to explain variations of PVG/GVI ratios in Coatepec, but respondent age did relate, non-linearly, with PVG/GVI ratios in Xalapa. In a nutshell, our findings indicate that the assessed physical and self-reported measures capture different aspects of urban greenery that differ in their potential uses, with GVI representing a helpful tool to quantify visible greenery at eye-level; GC being a highly informative physical measure to assess the amount of public and/or private urban greenery; and PVG as a quick and inexpensive measure of people's perception of visible urban greenery. Depending on the monitoring, managing, and/or planning goals, the use of the three assessed measures can provide an integral evaluation of urban greenery.