Simon — Viewing distance is a whole other can of worms. I considered addressing it in this piece, but decided to leave it for the sake of sanity. The ideal situation would be that viewing distances could be explicitly factored in, but obviously that’s a bit optimistic at the moment. There are also instances where one single viewing distance isn’t as relevant because there are many people viewing from many distances/angles. In such cases, knowing the real-world specifics of how big the display is will at least get you a rough idea of the situation.
I agree that knowing sizes in arc-seconds (or even estimated arc-seconds) is helpful, but in order to do that, I don’t think we should eliminate the ability to address actual device pixels. That is essentially what CSS “reference” pixels do.
myfreeweb — Yes, I am aware of such media queries. The problem with them, and the point of my whole article, is that they don’t actually correspond to actual physical resolution.
Josiah — I think you are misunderstanding my argument. It is less about making things the same across the board and more about making them different in appropriate and informed ways. There are indeed ways to know the size/distance of a projected image, but that is less of what I’m focusing on here.
For a more relevant example, consider the iPad and the iPad Mini. Both of them have the same resolution as far as a website can tell, but a website will render at completely different sizes between the two. Of course the viewing distances might be different, but it is not at all unreasonable to want to modify the design to better suit each device. Even if the apparent size (in arcminutes) is the same between the two when you factor in viewing distance, that doesn’t mean the same design will work just as well for both cases. For instance, I would probably want smaller margins on the iPad Mini than on the full-sized iPad. This example is even on the relatively subtle side of the spectrum. Resolution differences are much more vast between other kinds of devices, as Marcus demonstrated in his comment above.