It's a tough question. A sensitive issue. Something to consider carefully.
Whether in personal or business relationships, or in this case, admiring geese, close enough is good. Get too close, and you scare them away.
How do you know you are close enough?
Don't crowd their space, don't intimidate, or act in an aggressive or needy manner.
Be kind, loving, but not intrusive or nosy. If you step closer (literally or figuratively), and they stiffen, look away, clear their throat, check their watch, or give you any one of a hundred different nonverbal cues that says back off, then back off. People communicate so much more than with mere words. Words are probably only a nth. yes that's not even one percent of the communication process. Pay attention closely.
Of course each situation is different.
But is it really?
Listen to your senses. I could see the head goose getting a little fidgety. I could tell I was close enough. But I just had to push the envelope to see how close I could get.
In the end, it was my loss. They flew away.
How many times could we have had a little more quality time in that space, but we moved in too close and scared them away?
When you sense it, hold up. The quality of your relationship will improve, and your friend, kid, parent, lover, business associate, partner, or goose... will be more at ease.
When in doubt, try a role play with the family dog. They don't seem to mind it so much.