In response to increasing urban challenges such as environmental degradation, car dependency, and socio-spatial inequality, proximity-centred models like the 15-min city (FMC) have gained traction in planning discourse. This paper aims to (i) systematise the different approaches used to measure proximity, drawing on the framework proposed by Megahed et al. (Sustainability 16(3):1303, 2024); (ii) identify key indicators and metrics employed by the literature; (iii) assess which approach is more suitable to developing robust methodologies that enable the assessment of the FMC model’s impact on promoting equitable accessibility, urban sustainability, and quality of life. Six methodological approaches are examined: (A1) grid-based, which evaluates service reachability from spatial cells; (A2) POI catchment area, which defines accessibility zones around services; (A3) building catchment area, focused on proximity from residences; (A4) mixed-method, combining multiple techniques; (A5) network-based graph models, which analyse urban form through street connectivity; and (A6) index-based methods, which synthesise multiple variables into composite indicators. This categorisation is applied to a broad corpus of academic literature, identifying how each approach conceptualises and operationalises proximity. The systematisation clarifies the role of proximity within the FMC framework and offers a foundation for future research and planning, fostering more inclusive and context-sensitive urban strategies.