From Bill Bryson's A Short History of Nearly Everything:
Now, the first thing you are likely to realise is that space is extremely well named and rather dismayingly uneventful. Our solar system may be the liveliest thing for trillions of miles, but all the visible stuff in it - the Sun, the planets and their moons, the billion or so tumbling rocks of the asteroid belt, comets and other miscellaneos drifting detritus - fills less than a trillionth of the available space. You also quickly realise that none of the maps you have ever seen of the solar system was drawn remotely to scale. Most schoolroom charts show the planets coming one after the other at neighbourly intervals - the outer giants actually cast shadows over each other in many illustrations - but this is a necessary deceit to get them all on the same bit of paper. Neptune in reality isn't just a little bit beyond Jupiter, it's way beyond Jupiter - five times further than Jupiter is from us, so far out that it receives only 3 per cent as much sunlight as Jupiter.
Such are the distances, in fact, that it isn't possible, in any practical terms, to draw the solar system to scale. Even if you added lots of fold-out pages to your textbooks or used a really long sheet of poster paper, you wouldn't come close. On a diagram of the solar system to scale, with the Earth reduced to about the diameter of a pea, Jupiter would be over 300 metres away and Pluto would be about two and a half kilometres distant (and about the size of a bacterium, so you wouldn't be able to see it anyway). On the same scale, Proxima Centauri, our nearest star, would be 16,000 kilometres away. Even if you shrank down everything so that Jupiter was as small as the full stop at the end of this sentence, and Pluto was no bigger than a molecule, Pluto would still be over 10 metres away.
In light of that, and the fact that the solar system contains 8 planets, 5 dwarf planets, 335 moons and millions of asteroids, minor planets, comets, trojans, centaurs and the like, you really have to wonder why science fiction has obsessed for so long about interstellar and intergalactic empires. Isn't the solar system big enough?
One day I'd like to see a science fiction setting in which humans have colonised the solar system, but nowhere outside it - perhaps because travelling at the speed of light, or faster, simply hasn't been invented. This would be a fractured, multiethnic star system, where travel between planetary bodies takes weeks, months or years and communication is carried out by radio, and where military conflict is a projection of warfare on planet earth. In other words, a little like the era of European colonial expansion around the mid-18th century, except probably more likely dominated by countries such as China, India and Brazil.
Perhaps this setting already exists, and I just don't know about it. If so, its creators just haven't done a good enough job of getting it out there, dammit.