Two-Step Floating Catchment Area (2SFCA)
An accessibility method that compares supply and demand in two steps, so a facility serving thousands counts differently from one serving dozens.
Two-Step Floating Catchment Area, almost always written 2SFCA, measures accessibility by bringing supply and demand together instead of only measuring distance. It runs in two steps. First, for every facility, count the population inside its catchment and divide the facility’s capacity by that population, which gives a supply-to-demand ratio. Second, for every residential location, add up the ratios of all the facilities inside its own catchment.
The result answers a question plain travel time cannot. A doctor ten minutes away is not good access if forty thousand other people are also ten minutes away from that same doctor. 2SFCA catches exactly that, which is why it is standard in healthcare accessibility work and useful anywhere capacity is limited: schools, childcare places, sports facilities.
What it needs is capacity data, and that is usually the hard part. Without a number of places, beds or staff per facility, the method has nothing to divide, and a run that assumes every facility is equal is not really 2SFCA. Say which capacity measure you used and where it came from.