So, is the game entirely cell-based? I was stuck at the crash site, and I could not figure out how to go to another area....it seems like each area is a seperate "instance", and you need to use the map travel from the outskirts of the cell to get to another area. Is that the case?

Its like Fallout (and for modern games, Dragon Age: Origins). You use a 'world map' to travel. In order to get the world map option you have to move into a 'transition zone' - you will know you are there by the map icon changing to a blue globe.
Clicking the globe will bring up an interactive world map (unlike the one that is available by default from the map screen) - places you can go to will be marked as destinations, clicking on or near the location will create a walking path which you commit to with the red button on the lower right hand side of the screen.
For the crash site you want to head down and to the right a bit - you will see a monument/stone - at a certain point along that path Virgil will speak up about the world map.

I remember it being said when this game first came out that could walk from place to place. but it would literally take you 48+ hours to walk from one side of the map to the other.
Try to think of it more like oblivion and fallout than dragon age. you're always in the world map, however while in towns or places of interest, the town map takes over, you must first leave the boundaries of that map before setting off into the wilderness. even though the map shows black edges that must be passed in order to leave, you'll notice that the land itself is constant. A quick escape from a town is usually to follow the railwayline until the blue globe is shown.
A perfect example of this is to not open you're world map when virgil first asks, but to follow the rocky path. You may encounter some rather angry wolves which you would've simpley bypassed if the world map was used.
Also, as you're basically travelling very fast as opposed teleporting through the wilderness while using the map, you are vulnerable to being attacked along your journey. save often!

Added image for future reference . . . when blue . . . travel using the world map is available.
Also . . What is that question mark on the map?

You don't have to use the map travel system, you really can walk/run from point A to point B. That's why you cannot travel around the southern edge of the mountain range splitting the middle of the continent. To prevent you stumbling upon certain towns too early.
I wouldn't recommend it unless you where attempting to 'find' a town or area you already know exists but your character doesn't. Its incredibly boring for the most part. Unlike right the start with those wolves, its actually far safer (and a bit quicker in terms of 'game time') to manually run between areas yourself if you wish to avoid random encounters.
There are secret areas to find on the map that can only be located via manual travel through the wilderness. Not a lot of them, and I'd still recommend hitting up a walkthrough to find the general area of them rather than exploring all on your own.