Estimates only. Elevation is sampled along your route every ~0.4 mi from SRTM data (~30 m grid, ±~16 m vertical) and split into grade segments with the Douglas–Peucker algorithm — this captures climbs and dips a flat-average MPG misses, and matters most on long up-and-down mountain routes. Sampling finer changes the result by <1–2% (below the data's own accuracy), so we don't. Real-world mileage still varies with driving style, speed, wind, temperature, AC, tire pressure, traffic, and load.