## 2 Materials and Methods
### Method A: Literature Review of Circular Economy in Life Cycle-Based Policies and Studies  
A literature review was performed searching for circularity in life cycle-driven urban policies, with the first term standing for WHAT and the second for WHERE. The complete search string was Circular* AND (LCA OR (life AND cycle) OR LCC) AND (urban AND (policies OR environment OR studies)). The two most reliable and complete databases were selected: Web of Science (WoS) and Scopus. These two databases are widely regarded as mainstream bibliometrics tools, offering comprehensive coverage of subject areas, and being regularly maintained and updated by professional organizations. As a result, they are recognized as high-impact and trustworthy search engines [25; 26]. The string was searched in the database by topic (title, keywords, and abstract) with the following filters applied:  
* Time: From 2014 to 2024 (10 years), as it represents the timeframe in which the topic has emerged and rapidly diffused in policies. * Language: English. * Type of document: Research articles and review articles. * Types of work: Articles, review articles, and book chapters. * Research area/subject: Environmental science; energy; engineering; social sciences; business, management and accounting; materials science. The search was performed between January and February 2024; records published after 28 February were not included. The search was reported through the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), as shown in Figure 2, which was assumed as a structured and well-established procedure for phase A1. The scope of this study was not to perform a systematic literature review, but rather to conduct a systemic screening of current studies to map the main barriers and drivers cited in field positioning and then linking these with results from Method B (tools). Therefore, it is important to clarify that PRISMA guidelines have been adopted only as a reporting scheme for record selection and not for following its whole structure for reviewing purposes. According to the PRISMA diagram above, a total of 189 documents were retrieved from WoS and Scopus, including 36 duplicate documents. So, a total of 154 records were included in the first stage of the literature. A first round of result visualization was launched through VOSViewer version 1.6.20, an open-access and easy-to-use software that helps identify and visualize trends, patterns, and clusters of recurrent topics in bibliometric networks [27]. The totality of papers was entered into the software by selecting the analysis on word co-occurrence with keywords; fractional counting was then selected, and five was  
Figure 1: Workflow diagram of the whole methodology. the minimum number of term co-occurrence to be shown on the map. A cleaning phase was also performed, checking the totality of considered words and adding a thesaurus file, which forced the system to exclude terms that were not relevant to avoid duplications (i.e., singular and plural words), double-counting (i.e., with abbreviations), and synonyms and near synonyms (i.e., life cycle assessment and life cycle assessment). Optimizations were also performed in the scale of visualization to obtain the best possible results. The weights were performed with the total link strength. Afterwards, titles and abstracts of these records were screened and 92 were excluded: 80 because they pertained to other research fields (i.e., not built environment-related: ecology (10), agriculture or urban agriculture (16), rainwater harvesting and wastewater (3), sanitation (2), agro-industry (2), chemical industry (1), just to name a few); 12 because they were out of scope. From the remaining 62 records, recurrent topics and/or relevant ones are clustered--per common topics and scale of application--to feed a first qualitative analysis of results.