From Post-Apocalyptic RPG wiki
This document describe the basic game design for PARPG. The point of the game is to survive the encroaching ice age (at least for a couple of years). The game has two main elements; the "wilderness" map and the "local" map, representing different scales of interacting with the game world. In general, one travels from place to place on the wilderness map (aka world map) and interacts with people and objects on the local map.
Encroachment of Ice Age
The Ice Line
At the start of the game, the "Ice line" is somewhat north of the player's position, just off map. As time progresses, the line will move south (representing Earth's transition into the next ice age). The line can be considered "the arctic circle" (already several hundred miles south of it's current location in real-life temperate earth) ever expanding southward (and northward from the other end, but our game isn't that big!). The player can survive for short periods of time above the ice line - and in fact may have to undertake missions that force this. However, there will be no mechanism for generating significant amounts of food, so the player will eventually starve or move south. If he doesn't freeze to death in a blizzard first. All NPC locations will decay over time once the line passes them. I might be very interesting to model this process in terms of declining town population, increased banditry, increased refugee/migration encounters.
Note that the "time scale" of this feature is critical to the game. If the "Ice Line" is going to cross the location you are in in 4 weeks, then you have that much time to "finish" the quests in that area. In this way we force the player to manage his game time as a resource. This is CRITICAL because of the use-based/training based skill system.
As outlined above the lack of food makes a natural "soft" barrier. The hard frozen north will 'naturally' become boring and (eventually) deadly to the PC, so he is forced to warmer/more interesting areas. It might be worthwhile (or maybe just cool) to implement a hard barrier of a 30' high glacier that is literally impassible. I don' t think the "game" needs this, but I find it a cool visual to think of reaching "the northern end" of the world. One reason I disfavor this idea is that I find it frankly unrealistic that "enough" ice could accumulate over the course of the game to make an essentially impenetrable ice barrier. Another option would be to just have this be the "original" northern border of the map - representing 20-odd years of ice accumulation, but not have it move during the game.