Comparability is not a property waiting inside urban cases; it is produced through decisions about scale, duration, field boundaries, evidential form and the terms under which difference is permitted to remain legible. A neighbourhood, a mobility trace, a physiological response or a transnational urban comparison becomes comparable only after an apparatus has defined what counts as the same kind of observation across changing circumstances. Wang et al. show that street-view imagery, social-media traces, positioning data, physiological signals and video are not interchangeable windows onto a single urban reality: each data type constructs a specific evidential object, with characteristic gains in scale, granularity or continuity and equally characteristic blind spots, biases and interpretive limits. Gerlofs and Poon make the same problem visible at neighbourhood scale, where cartographic, statistical, photographic, archival, historical, narrative and geospatial records cannot simply be aggregated without confronting commensurability, replication and territorial definition.
