Knowing when you are overflying something

How do you know when you are exactly overflying a specific spot on the ground?
It's it just a matter of knowing your particular aircraft, or are there tricks
that can help to determine this? I know you can look off the tip of your wing
to see if you're abeam something (such as a runway), but how can you tell when
you're right over something? I presume there's no way to look straight down
from most aircraft, and it seems like the view over the nose is often several
miles away.

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