It's using some hybrid of isochrones & walking time "as the crow flies." The subway travel is in isochrones, but once you exit the subway the walking time assum

It's using some hybrid of isochrones & walking time "as the crow flies." The subway travel is in isochrones, but once you exit the subway the walking time assumes walking in straight lines with no obstructions in any direction. So yes that's inaccurate but it's relevant that only the walking time is done so. I assume subway ride time is based on subway schedule times.