Describe entirety.
I know what it takes to get from Los Angeles to London, distance-wise, time-wise, & route-wise. Because I've done it. Apparently you live in a world where you would have zero clue about that.
Would it be your contention that I did not fly the route that I flew, the distance that I flew, and the time it took to do so?
Let me try and make this a bit more clear.
You may happily navigate to a destination based on the map you were given, in a small area.
Let's use the UK as an instance.
You can get to every part of it by using maps or generally GPS, assuming GPS works for certain areas...which it is getting better the more ground positioning stations that are set up to cover the areas.
Ok, so you can confidently accept that you're getting to where the map tells you.
This is fine for an island, just as it's fine for you to go walking around your area without a map, just by committing your routes to memory but to an outsider, they would require a map.....initially.
Does any of this give you the shape of the Earth you are part of?.....Obviously, no.
Now you can continue to follow maps of what you're told about in your known world and all you are doing is hopping from island to island or continent to continent...which again, is fine.....but does it give you the shape of the Earth you are part of?........Again.....no.
Then you have the oceans.
Mapped?
In a fashion, right?
Point to point navigation.
Does this give you your Earth shape?......Once again....no.
So therefore, what you think you know is based on maps set out for you and navigation to points.
It does not mean you navigate over a ball/convex curve and you certainly do not know the entirety of the Earth you are following navigation routes for.
In a nutshell, you've travelled in planes, trains, automobiles and by sea.....probably.
You are a point to point observer of what you can follow and totally oblivious to what you cannot.