Allegiant question

In book one of the Divergent series it clearly states that the Abnegation faction only eats frozen or canned food because the farms are far away.

Well....that dosen't make any sense now does it?

Because literally everything in their society is in one city.

And in Allegiant, Tris and Four go to the outskirts of that city in under a day.

So unless they were already under the implication that there was life outside the city walls-

Which they weren't.

And somebody was delivering them food...

This statement creates a plot-hole.

I'm confused. Somebody explain this to me!