To continue with your metaphor using the Forth, if your project is to get from North Berwick to St Andrews, and you chose to estimate it "as the crow flies", yo

To continue with your metaphor using the Forth, if your project is to get from North Berwick to St Andrews, and you chose to estimate it "as the crow flies", your result would be about 20-30km. Whereas, if you chose to traverse the Forth up to Stirling, then return along the northern coastline, you'd be looking at 200km. The Firth of Forth is visible with the naked eye from the ISS though. So picking a resolution that misses that geological feature and making an estimate for crossing the Forth that's out by an order of magnitude would be transparently and self-evidently incorrect... Particularly if you and your team are on the bank of the Forth when you make the estimate. Picking an exact resolution is challenging, but picking a "good enough" resolution that minimises "out by an order of magnitude" errors really isn't for most tasks unless you're taking part in the most cutting edge of research.