Implications of the modifiable areal unit problem for assessing built environment correlates of moderate and vigorous physical activity

• Examined momentary exposure to environmental factors during walking periods.
• Green space and land use were associated with activity level during walking periods.
• Compared results using three buffer- and three grid-based scales of aggregation.
• Scale remains an important consideration when measuring the context of physical activity.
• Findings help understand the sensitivity of environment–activity associations to scale.

This study assesses the influence of the Modifiable Areal Unit Problem (MAUP) in analysis of the effect of built environment (BE) exposure on moderate and vigorous physical activity (MVPA) during walking periods. Adults (n = 55) wore a GPS unit and accelerometer for up to 7 days. More nearby green space, residential use, and open space were positively associated with MVPA after controlling for socio-demographics. Scale and zoning effects were observed in models of momentary BE-MVPA relationships using different scales and zone configurations. Compared to larger aggregation zones, proximate measures may be better for assessing green space and land use exposure during walking periods. Results do not support a prescriptive recommendation whether future studies should use a buffer- or grid-based zonal configuration.