A novella about what if part of the earth of 1962 got transported to the surface of a huge, infinite disk with millions of continents, and what happens when the US / USSR begin exploring this world.
It has some great ideas:
What would it be like to settle a million continents? (I'm thinking lesswrong style waves of colonizers, each with a speed, racing across the land and gradually separating into waves grouped by speed)
What would it be like if a mercator map actually was reality - if siberia really was far, far away from alaska (if the map was drawn like that), or what if australia really was in the SE corner of the world, incredibly distant from north america.
What would it be like if there were always a new frontier, and would be for a million years?
What if the world were so large that you could fly in a straight line for 20 years and not reach the end?
What if the physical constraints binding us to a planet were much, much stronger - if gravity didn't decrease with altitude. No matter how sophisticated our technology gets, we may not be able to ever get into space (or use satellites)
The world exploration theme doesn't get fully developed (the book's not long enough) but I still really liked & felt inspired by the story. Charles Stross is becoming one of my favorite authors. I always thought of him as genre, and he is kind of workmanlike in interviews / on his blog, but actually he's got a ton of great ideas.