Coverage analysis
What 15 minutes covers in Columbia.
Three-river-bounded and military-base-clipped, Columbia isochrones radiate along the interstate spines in a starfish pattern from the I-20/I-26/I-77 hub, with the Congaree and Fort Jackson eliminating westward and eastern expansion respectively.
At 15 minutes, the Columbia isochrone captures the standard trade area — a zone where trips are planned but customers are willing to cross neighborhood boundaries. Unlike a 30–80 km² in typical US metros; the range varies 3× depending on road density and barriers circle, the real road-network polygon follows Columbia's actual highway corridors, accounts for bridge and interchange chokepoints, and respects the natural and built barriers that force drivers to detour.
Best-fit categories at 15 minutes: Casual dining, specialty retail, auto service, full-service salon, pet supply. The 15-minute isochrone is the standard input for franchise disclosure documents and protected-territory negotiations.
The city-level population of 136,632 and a median household income of $54,000 give a sense of Columbia's economic density, but the figure that matters for site selection is the population inside the polygon — not the city as a whole. That number shifts dramatically depending on whether you're drawing from a high-density urban core or a lower-density suburban corridor. Use the tool above to set your actual candidate location, then generate the isochrone to see the real catchment.