Comment by diggan
Probably not scientifically accurate or anything, but if you point somewhere, then "straight" is in that direction. I guess it'll loose accuracy as you get further and further in the distance of the direction, but probably for most people would be good enough for "straight in that direction" :)
An actual straight line would be tangent to the earth at that point, so I don’t think that would work well for anything over a few hundred miles.