Hypothetical question:
Assuming at a moment in time one is momentarily blind due to mist/cloud/fog patches and choose to zoom onto the highest resolution of the Garmin 430 moving map, if trying to follow the centreline of the Thames around the bends between Vauxhaul bridge and the London Heliport (2 miles?), how accurately is that map going to stick you in the middle of the river throughout?
Subject to speed and height, what margin of error would there be, solely relying on that Garmin alone to take you accurately down the river centreline around those bends?