If a coordinate is stored in a geographic coordinate system, it's quite easy to calculate the following things exactly:
- Distances (geodesic)
If you store the coordinates in a projected coordinate system, these things are calculated in a Euclidean way, which means there will be huge distortions if your map covers a larger area of the earth.
So, in my view, storing the coordinates in a geographic coordinate system has the
- advantage that all calculations can be made exactly, and the
- disadvantage that they must be projected before they can be rendered in a map.
Since the latter is something that can be done very fast on modern processors, I don't think it would ever be a huge disadvantage.
Are there any other disadvantages? If not, then why does one ever store geographic data in projected systems?
One answer to the second question could be that the projecting of coordinates was not always so cheap. On processors of the 70s, it could be better to store the coordinates in the way they are rendered, to avoid having to project them every time the map is rendered.