Well you start to get into the area of philosophy and metaphysics fairly quickly don't you? Plato v. Aristotle and all that stuff. What is the relationship between the Universal and the Particulars, or in this case between the mathematical concept or 'Form' of a line and its practical applications, attributions or "accidents" in nature, etc. It brings in all sorts of interesting words like resolution, scale, approximation, perspective, viewpoint, etc. Or you can go sideways into Kantian philosophy and start talking about perceptual grids and how our mind's interpretation relates to objective reality, etc. Is there no such thing as a line, except in our thoughts? Is it just a concept we impose on nature?
What Fal said, it depends a lot on definition. It's largely a matter of semantics and context.
