So for generations a ship has been traveling through space. After reaching their desired destination you are left with a group of people who have been used to their largest spaces being no more than a few tens of meters across.
If I were to suddenly send them out to populate a planet with vast swathes of land where you can see for miles I would expect some degree of agoraphobia.
In my story I want the arriving population to only have a minority without this fear. How would be best to explain/provide a counter measure to the agoraphobia?
The causes of this fear would be, of course, the unknown:
Information overload: I imagine seeing for miles rather than only a few meters would be difficult to process if you lived the majority of your developing life on the ship.
No fixed paths: The ship would have been huge but to reach somewhere you only had to keep to a (probably well sign posted) corridor. The contrast a planet's surface provides is huge - the fear of getting lost would probably also be so.
Routine: I don't imagine there is much variation in where to go on the ship, the change in what you're doing and where you're going is a cause of much distress to most people suffering from agoraphobia.
It isn't abnormal: In our society treatment for agoraphobia often includes being assisted by someone who knows and understands your problem but doesn't have it themselves. This wouldn't be possible if you are one of the majority - they may not see it as a problem.