Comparing greenspace metrics and buffer methods in Metro Vancouver, Canada: Implications for environmental health research

BACKGROUND & AIM: Access and exposure to greenspace has been shown to promote mental and physical health; however, not all studies have found these benefits, with some studies reporting no association and others reporting associations with adverse health outcomes. It has been suggested that the use of diverse greenspace metrics, the varied quality of these metrics, and the specific methods used to quantify exposure or access, may contribute to these inconsistent findings. This project sought to compare the results of using different metrics in Metro Vancouver, Canada. METHODS: Greenspace metrics were calculated from the centroid of each 6-digit postal code. Average buffer normalized differences vegetation index (NDVI), green landcover, tree canopy cover, and park count were calculated using circular and network buffers, at both 400m and 1000m. Pearson’s correlation coefficients were calculated to compare the results for each metric and method. RESULTS: The number of parks was only weakly positively correlated with each of the other three greenspace metrics for 1000m circular buffers (NDVI r = 0.12; green land cover r = 0.07; tree canopy r = 0.14, p < .01). For 1000m network buffers (NDVI r = -0.34; green landcover r = -0.12; tree canopy r = 0.05, p < .01) two of the correlations became negative. Circular and network buffer were most highly correlated for the tree canopy (1000m r = 0.92; 400m r = 0.86, p < .01), whereas park count had the weakest correlation (1000m r = 0.66; 400m r = 0.66, p < .01). CONCLUSIONS: The associations between greenspace metrics vary. Selection of buffering method may be particularly influential when using park count data. These findings support the importance of intentional selection of greenspace metric and measurement method in environmental epidemiological research. KEYWORDS: greenspace metrics, NDVI, tree canopy cover, parks, network buffers, and circular buffers