Just read somewhere that the shortest path between two locations is an arc and not a straight line! eli5 how an arc is the shortest path for planes.
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The arc is the shortest path between two locations on earth (on its surface) because the earth isn’t a flat plane.
On an ideal flat plane the shortest path between two points is straight line.
In the real world you live on a globe that only comes close to being flat at very small scales.
On the globe the shortest distance (on the surface) between two points follows a great circle. A great circle is one the divided the globe into two equal halves.
you can draw a great circle through any two points on a sphere so that the shortest path between those two points lies on the great circle.
Depending on the scale and your map projection it may even look like a straight line or it might very much not look like one.
Technically you could always have the shortest distance be a straight line by tunneling though the earth instead of along it surface, but that doesn’t really work for most airplanes, ships or cars, that people use to travel between points on this globe.
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