Triremes CAN travel more than 3 squares at sea; they just have a 1/2 chance of getting "lost", dropping to 1/4 with Seafaring and 1/8 with Navigation. Five squares is only one turn at sea, which is very doable; prioritizing sea techs is also doable once you have 4-6 cities (you can probably squeeze a couple in ICS-style). I believe the "known map" option does not show all units and all cities all the time (correct me if I'm wrong); I thought it was more like the Apollo snapshot where you see all the landforms and existing cities. Playing the world map "in the dark" with a random start can be interesting trying to figure out where you are (I thought I was in North Africa once; turned out to be Australia...). Another thing to consider is that the AI ALWAYS knows the full map, as well as wherever the other players are. I have seen AI civs make beelines through unexplored territories to take out another civ early in the game. And for the sake of newer players a world map or known map start can help them plan things out. I also would like to see a few maps that are more water than land, which would probably mean hand-made as the generator does not do small islands well. The few I have played have been interesting for the naval aspects of war and trade. I would probably go for more like 10 squares between islands (zig-zag layout?) and 6-8 cities per island.