Urban Streetscape Changes in Portland, Oregon: A Longitudinal Virtual Audit

Streetscape imagery has considerable potential for observing urban change. The literature lacks sufficient longitudinal studies, however, on urban change considering human perception and activities. We conducted a longitudinal virtual audit to observe the change in urban liveliness, human activities, and built environment by examining streetscape imagery taken in the late 2000s and the late 2010s in Portland, Oregon. Eleven untrained crowd workers were recruited to provide liveliness ratings of 24,242 streetscape images for both periods. Tabulation, mapping, and multilevel regression analyses were conducted to observe the distribution, changes in liveliness, and the factors affecting these changes. The results confirmed that the city had become livelier during the ten-year study period, which was spatially associated with the increase in pedestrians and cyclists and particular elements of the built environment, such as mid- and high-rise buildings and sidewalk signs. Although these results were somewhat expected, this study's value lies in confirming the potential of virtual audits conducted using Google Street View Time Machine for retrospectively examining subjective and objective urban change. Caution should be exercised, though, while interpreting urban change as temporal conditions (e.g., season, weather, and irregular events) can potentially bias the results in longitudinal studies.