Drive time vs radius
Two ways to draw the area around a site, and when each is good enough.
A radius is a circle of a fixed distance around a site. A drive-time (isochrone) area is everywhere reachable within a number of minutes on the road network. Drive time is more realistic where roads, rivers or highways split a city; a radius is simpler, faster and good enough for dense urban areas and first comparisons.
xMap Flows does both. Radii and drawn areas: points with a distance, places with a distance, and shapes you draw to follow a road or a river. Travel time: the Travel area block draws what can be reached from each place within a number of minutes, or a distance by road, by car, walking or cycling, and the blocks after it (Nearby places, Demographics) search inside it. When the road service cannot answer, it uses a circle at a straight-line speed instead and says the area is an estimate.