## 2 Literature Review
### Mapping People's Perceptions and Observing Interactions  
Through perceptions, people interpret unconnected stimuli to construct something meaningful about a certain environment [47]. [PERSON] [48] explains that _perceiving_ and _acting_ are fundamental to almost all complex organisms for sustaining life. Both processes operate synergistically. Perceptions and objective properties of places can be mapped and quantified using PPGIS [49; 50] methods, which identify relationships between environmental factors, local experiences and everyday behaviour [51; 52]. PPGISs have been used in various place-based studies, such as a combination of accessibility analysis with PPGIS of users' environmental perceptions [53], to map locations that enhance relaxation and reduce stress among university students [32], the multiple-level influences of health behaviours and factors that influence active travel by older adults [54] and the application of PPGIS for planning urban green infrastructure [55]. With PPGIS, more specifically VGI, the researcher can collect perceptual data while citizens act as active sensors within an environment [49].  
From a conceptual and research perspective, VGI intersects with the more established field of PPGIS in the development of Internet-based tools to create, assemble and disseminate geographic information provided voluntarily by individuals [49; 56]. The integration of Internet-based GIS and citizen information can reveal the strength of intersecting networks in community management, facilitate communication between different groups of stakeholders and empower citizens to participate effectively in the processes of urban planning and design and policy-making [57; 58].  
[PERSON] et al. [59] explain that the built environment engages humans not only through its locations for different physical activities and uses but also mentally, by providing opportunities for learning and meaning creation. Therefore, investigating real-life situations with VGI perceptual data and observing interactions between people and the built environment are effective ways to understand human behaviour and needs [60; 61]. Observations provide insights into how people, objects, artefacts and other features of the built environment interact [62]. With observation, it is possible to collect and analyse information about physical aspects that influence the frequency of VGI-mapped perceptions. It is a useful resource to subject practical actions and activities _in situ_ to detailed analysis [63].  
Observations of interactions between people and the environment have been empirically tested in various urban design and planning studies looking at 'flexible spaces' [64], 'life between buildings' [65; 66], the sense of community in campus public spaces [8], 'urban design features' [67], 'landscape taxonomy' [68; 69] and the 'post-occupancy evaluation (POE) of outdoor spaces' [70]. Such observational studies suggest that the urban design of creative clusters, such as university campuses, should promote combinations of urban forms, city blocks, building types and frontage types that suit combinations of land uses, activities and people [6].