Exploring centricity of activity spaces: From measurement to the identification of personal and environmental factors

It has been known for long that people tend to form clusters of activity places, typically around their daily life centers, for a number of reasons such as to facilitate their daily mobility. Despite this knowledge, there is little research done on identifying and measuring this type of travel behavior. The exiting measures of activity space dispersion often exclusively rely on overall numeric assessment and overlook the geographical distribution of activity places. In this study, we introduce centricity as a new dimension of activity spaces and we operationalize it as a clusterization of activity places. Delineation of clusters in this approach adds a spatial component to the measure. This enables the scrutiny of activity clusters and possible personal and environmental factors contributing to their formation. Furthermore, using data collected through an online mapping survey, we study the centricity of individual activity spaces and classify them into three groups of monocentric, bicentric, and polycentric. Our study of citizens of Helsinki metropolitan area aged 55-75 shows that monocentric activity spaces are the most common type among the study group. Nevertheless, a considerable share of extra-neighborhood travels are made to denser areas of more urban characteristics. The results do not indicate any significant associations between socio-economic characteristics and centricity. However, urban form and travel mode were found to be significantly associated with centricity. Overall, the findings show that use of centricity can help broaden our understanding of individual travel behavior and in turn contribute to interventions promoting healthy and sustainable travel behavior.