Network Buffer Analysis
Definition
Network buffer analysis delineates areas reachable within a specified cost along a network—commonly called isochrones for time or isodistances for length. Unlike Euclidean buffers, which draw circles around locations, network buffers expand along passable streets or paths, respecting one-way restrictions, barriers, and slopes. They show the footprint of access from an origin by car, transit, bike, or foot, often at multiple thresholds (e.g., 5/10/15 minutes). Method choices include exact isochrone algorithms or approximations via sampled paths; outputs can be polygons, lines, or grid-based surfaces indicating cumulative opportunity. Properly built, network buffers provide a fairer measure of access to services than simple radii and are vital for equity audits and compliance with standards such as walk-shed requirements around stations.
Application
Planners evaluate pedestrian access to schools, parks, and transit stops. Retailers estimate realistic trade areas. Health agencies measure walk-to-clinic coverage accounting for crossings. Emergency responders plan response rings by time-of-day traffic. Event managers plan crowd egress. Trail designers estimate hiker reach from trailheads given terrain difficulty.
FAQ
Why not use circular buffers for access studies?
Circles ignore barriers, cul-de-sacs, rivers, and slopes. Network buffers mirror real travel possibilities, often shrinking or skewing the access area compared with a radius.
How granular should time thresholds be?
Use a small set of actionable bands (e.g., 5-minute steps) rather than cluttered gradients. Align with policy thresholds or service-level commitments.
Do isochrones work with transit?
Yes—time-dependent networks incorporate schedules and transfers. Results vary by departure time, so publish multiple scenarios or a band of typical access.
How are steep slopes handled in walk-sheds?
Assign slope-based impedance to edges using DEM-derived grades. Paths with excessive grade can be penalized or excluded to reflect accessibility realities.