One of the givens in any space opera is the ability to move through space (relatively) quickly from one place to another. Some people use worm holes. Others use plain old hyperspace. In the Star Wars universe moving from one star system seems to be a bit like driving your car across town. Sometimes stories are written about generation ships which travel through normal spacetime over incredibly long time frames.
That's all well and good. But there aren't any roads in space. Of course, all those ships transporting people around have wonderful navigation systems. The issue, though, is that distance and direction on planet Earth are all based on constants. Locations on the surface have precise coordinates, given in latitude and longitude. Latitude is based on the distance north of south from the equator, and longitude is based on the distance east or west from a given base line (0⁰) which we humans have decided passes through Greenwich in the UK. In the past, longitude was found to be exceptionally difficult to measure. It wasn't until the invention of extremely accurate clocks that we could get it pretty right. To quote Wikipedia "Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time (UTC)." It's an over-simplification, but we don't need more than that for this discussion.
The point is that in order to navigate between two places, you need to know the position of those two places based on two 'knowns' – your start point, and your end point. Sure, you can recalculate en route. Aircraft do it all the time, because they work in three dimensions: latitude, longitude and height. I assume submarines do, too. If we look at space, working out how to get to other planets has already been done successfully many times. But the further we go, the harder it gets. This io9 article explains it better than I could.
So why do I care? Because my current WIP is very much about following a specific journey made by space-farers in the distant past. There aren't any roads, so I need breadcrumbs, or a ball of string, and I'm not sure how to make it work.
Ah well. That's one of the joys – and the frustrations – of writing science fiction.