The neighbourhood unit is used extensively across numerous disciplines to empirically measure various urban characteristics and phenomena. Spatially heterogeneous system variables-e.g., environmental, sociodemographic, infrastructural etc.-create distinct local-scale subunits, or neighbourhoods, within cities and other larger urban systems. Reflecting unique contextual features at the local scale, the way in which such boundaries are drawn can influence measured outcomes like health, wellbeing, and sustainability, which in turn can have an impact on decision-making. With Geneva as our case study, we compare two different conceptualisations of the local neighbourhood: (1) functional neighbourhoods established using a data-driven approach that emphasises the built environment and neighbourhood functions; and (2) perceived neighbourhoods whose boundaries are drawn by Geneva residents through a spatially explicit web survey. In this comparative analysis, we employ geospatial analysis methods and develop indicators to characterise the relationship between functional and perceived neighbourhood boundaries for a group of Geneva residents. Results suggest that there is little consensus between the functional and the perceived neighbourhood boundaries although both are expressed at the same spatial scale. While there has been increasing evidence showing the importance of local-scale approaches in urban systems research, the conceptualisation and operationalisation of locality remains arbitrary and ambiguous. Here, the choice of the local neighbourhood unit when studying urban systems is also discussed.