## 1 Introduction
Potential challenges to test this hypothesis in relation to urban planning and design include the following factors: (1) it requires multidisciplinary and interdisciplinary approaches to unpack the current knowledge of loneliness and its relation to the built environment; (2) there is a lack of effective tools to document and measure the experience of loneliness and overcome the high stigma perceived by many individuals about sharing their experiences; (3) the subjective nature and transient state of loneliness makes it more challenging to identify specific planning and design efforts that may be of relevance to loneliness and assess the effectiveness of measures taken. The purpose of the present study is to find pathways for urban planning and design to address loneliness, given the aforementioned challenges. A proposed first step to test the hypothesis is to investigate how people perceive public space and whether people use public space in situations when they feel lonely. This study employs the multiple sort task (MST) method to explore these issues. The MST [38] was first developed in the field of environmental psychology. It was previously applied to help individuals to articulate their perceptions of \"multi-attribute domains\" [39] such as architecture styles, casino space, etc. and to ultimately reveal their conceptual systems. This makes the MST of great potential for investigating conceptualizations of places and their relationship to loneliness. The core reason for choosing MST is that, following a long tradition in qualitative research, it is a mechanism of empowering respondents to use their own words/expressions to reveal the knowledge. The study included two relatively small samples with the aim of testing MST's viability for exploring people's perception of public space and its potential for people who are vulnerable to loneliness in the Stockholm context. While striving to promote itself as a leading sustainable city [40], Stockholm inevitably faces urban transformation challenges in terms of hosting a growing urban population, an aging society, a housing shortage, and serving as the capital of the country which has the highest number of single person households in the EU [41]. The paper gives a detailed account of how the samples were developed, conducted, and analyzed. Each sample included six participants of varying ages and backgrounds. Each person was provided with 20 color photographs of different public spaces in Stockholm. They were asked to assign the photographs to different categories that they developed themselves. They were requested to put the photographs into distinct groups on the basis of the activities they anticipated would occur there. The data were collected in a qualitative fashion. On average each individual MST procedure was performed over 30-40 min (_Sample One_) and 60-80 min (_Sample Two_), including the sorting and commentaries by the participants of the ideas behind their assignment of places to categories. A multidimensional scaling procedure (MSA) was performed to quantitatively analyze the underlying structure across the combination of the six responses for each sample. The content of the commentary was analyzed to elicit associations to public space in relation to loneliness. The relatively small sizes of the samples presents a potential limitation to generalizing the theoretical implications of the results. However, despite these possible limitations, the results of these samples showed coherent structures with interesting variations between people. A general multi-purpose set of places were identified, with others being differentiated in terms of whether they were 'hard' or'soft' and 'open' or 'enclosed'. Public spaces were conceptualized differently when respondents considered conditions under which they felt lonely. An assemblage of public spaces that are relevant for people when they are in situations of feeling lonely were identified, though these were slightly different for the young adults of _Sample One_ when compared with the elderly of _Sample Two_.