[This is the best online dream description I've ever seen, originally published at this now dead link, and preserved here in case the Web Archive goes down.]
I had this fucking wild dream this morning. Me and maybe three other people I know somehow got sent forward in time. I would say it was about ten or fifteen years in the future. When we got there we met up with this woman who gave us our mission, which was to get up to Canada and rendezvous with some sort of rebel forces up there. We were in NYC, and had to make our way north from there. Since that's such a big transportation hub, that should have been no problem.
But this was the future. Things had changed. New York City had been divided into northern and southern zones, via a gigantic wall and forcefield. The southern half still had people living and working in it. But the northern half was completely off-limits. The official story was that aliens (space, not illegal) had taken over the northern half of the city, and the rest of the United States northward.
We knew, however, that this officially story was largely a fabrication. But that was all we knew. We had to roam about the lower half of the city, trying to find a passage to the north. And we had to do so without arousing any suspicions, which was an extremely difficult task. No one in the city would answer questions or help us.
And the police presence was total. You had to keep moving at all times. Any group of people who were stopping to talk or otherwise congregate was quickly spotted and broken up by patrolling police. The right to free assembly had obviously been revoked. The sirens of the police cars also had been engineered so that they played the tune of "America the Beautiful." The police also had flying discs which they sent out after you. They were autonomous electronic devices which hovered and would track you as you ran. Once they were within range, they would fire an electric bolt at you to incapacitate you until officers arrived. The discs were called "temperplexes," and they were all apparently controlled by larger motherships which flew higher and basically looked like UFO's.
The implication, of course, was that somewhere in the future, the country had gone under martial law - perhaps during a faked alien invasion (or maybe a partially real one, I don't know). During this time, large segments of the country had been sealed off completely from one another physically and with all communications. Presumably, people living in each zone were told that all neighboring zones had been completely overrun by the aliens.