Comment by gonzus
13 hours ago
One of the advantages of doing this seemingly weird projection is that you can treat "local" maps (for some definition of local) as flat rectangular grids without introducing a lot of errors: drawing straight lines between two points, measuring the distance / angle between them, etc., just by dealing with a flat piece of paper. VERY convenient, but the farther you are from the center of the projection, the higher the errors that are introduced.
In short, you can treat the local geometry as Euclidean.
Or, to put it simply, the shape of the Earth can be considered flat for local mapping purposes.
If grid north and true north are the same everywhere, it would be proof the entire Earth is flat.
If your planet is tiny, it's very easy to figure out that it's a ball, a child can see it with their bare eyes. The planets in "Outer Wilds" are like that.
Because this planet is larger, smart people trying to figure out how it works used simple tools and measurements to conclude that it's a ball, we know that Greeks and Romans figured this out, I'm sure other civilisations did too.
Greg Egan's "Incandescence" has people who live somewhere where you can discover, in this same way, General Relativity. There's a small but noticeable difference between the simple linear results we'd see for Newtonian physics in rudimentary experiments and what they can observe and they figure out why. Since they have no context for what it means to observe this and have (to their memory) always lived somewhere this happens, they aren't terrified by this discovery any more than we were terrified to discover how our Sun must work - so much hydrogen in one place that it undergoes spontaneous nuclear fusion which releases so much energy that we can easily see by it even after it is no longer directly visible, OK cool, I still need groceries.
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