In order to compare self-assessments with the binary GIS assessments, we dichotomized the self-reports by taking 'totally not agreeing' and 'not agreeing' together as perceived 'absence' of the green neighborhood quality and 'agreeing' and 'totally agreeing' were taken together as perceived 'availability' of the quality.
GIS assessments of the five green qualities (Additional file 1: appendix 1) were based on the National Land Survey of Sweden (Lantmäteriet) that is part of EU program CORINE [ 29] in which the land and vegetation cover was mapped into approximately 58 classes.
Another explanation for the low agreement could be that the definitions used for the GIS-assessments were more extensive, and consequently more restrictive, than the phrasings used in the survey questions.
Convergent validity of SGS (individual and area-aggregated) versus the GIS-assessments 'as gold standard' were measured as correlation, using Spearman's rank correlation coefficient, as agreement, using the sum of sensitivity and specificity (for definitions see table 2) [ 32] and Cohen's kappa.
Still, an in-depth GIS pre-assessment would further enhance and refine the results.
cThere are already concepts of conducting a GIS-supported assessment of environmental sustainability and cost-effectiveness for crops on an operational level.
A GIS-based assessment of total solar irradiance for the year 2010 at the site of Becán showed that in general North and East facing walls of monuments received significantly lower levels of radiation, suggesting that the major impact of orientation is to affect incident levels of damaging solar radiation, ensuring higher availability of water for Trentepohlia colonization in low-irradiance areas.
a[ 25]; b[ 34]; c[ 23] (GIS-based assessment of cereal straw energy in the European Union – average value for East Anglia, UK).
Missing environmental data and a lack of precision in address histories form the primary limitations in GIS exposure assessments, so future studies could be strengthened by the systematic geographic tracking of environmental data and the ascertainment of address histories at the time of reportable diagnoses, such as cancer (Hurley et al. 2003; Wakefield 2000).
A major strength of our study is the use of an objective measure of traffic-related air pollution at residential addresses (e.g., GIS-based assessment of traffic density and distance to major roads) to capture exposure relevant for subjects living in close proximity to busy roads.
