Choosing projection for points if they extend outside of bounds

Question

I have a project where there are GPS points that are centered around the Chesapeake bay, with some points extending between North Carolina and southern Canada

I have been using the NAD83 Virginia South state plane because I was told that a projected coordinate system is more accurate for distance calculations, but I am unsure if this projection would be reliable with the spread of my data points.

I read that outside of a specific state zone errors increase quickly, but I couldn’t find any information on how error accumulates if points extend outside of the bounds of the state zone (for example, for every 5 km outside of the state zone you’d see error increase by 1 m).

Do you know if this information is available anywhere, or am I misunderstanding how the error works? Would a more general projection for all of North America such as the North America Equidistant Conic be a better choice?

Answer 1

Because the earth is a 3d sphere and our map is a 2d piece of paper then we will always have distortions when we move from one to the other. These distortions can be in angular conformity (are angles correct from a certain point), distortion in distance (is everything on the map the correct distance from a certain point) or distortion in area (do areas on the map represent true areas in the real world). Some projections just sacrifice one of these components, whilst others sacrifice a little bit of each for general accuracy. Most sections of the world have there own system to limit these distortions and as you get further away from the central point then these distortions get larger and larger. The system that you choose will be dependent on what's the most important to you i.e. angles, distance or area. QGIS have a good guide that might help you decide: https://docs.qgis.org/3.10/en/docs/gentle_gis_introduction/coordinate_reference_systems.html