Planning is increasingly called upon to address health inequalities, yet the analytical tools used to measure accessibility are often under‑examined. This paper focuses on the methodology used to construct walking isochrones for people aged over 65 in Northern Ireland, demonstrating how methodological choices fundamentally shape understandings of access to community pharmacies.

Drawing on doctoral research, the paper critically interrogates the widespread application of the “20‑minute rule” as a benchmark for accessibility. Despite its prominence in planning discourse, the rule is rarely defined or empirically grounded, particularly in relation to older populations. This research develops a walking isochrone methodology that incorporates age-sensitive assumptions, including adjusted walking speeds, network-based routing, and the influence of terrain. These refinements enable a more realistic representation of how older adults navigate the built environment.

The findings illustrate how standard approaches, often based on simplified speeds and uniform thresholds, risk overstating accessibility, particularly when applied uncritically to walking. Small methodological variations produce markedly different isochrone outputs, reshaping the geography of perceived access and revealing spatial inequalities that are otherwise concealed.

The paper argues that isochrones are not neutral technical tools but constructed measures that embed assumptions about mobility, capability, and space. By making these assumptions explicit, the research contributes to methodological innovation within planning and calls for more reflexive, context-sensitive applications of accessibility metrics. In doing so, it aligns with the conference theme by demonstrating how strengthening methodological foundations can enhance planning’s capacity to identify and address inequality in ageing populations.