I have come to the end of a grid with no connecting grids north or east and will have to turn back south to continue my journey. The grid I am on is Gloaming Vale and the edge is at x=256 and y=256. Computer people out there will get the meaning of that right away, non-computer people would be wise to see it as a pointless fact.
Second Life presents the lack of a connecting Grid as a vast sea. This makes isolated Grid spaces presented as Islands. Since the sea is just a symbol of nothing you can't enter it, and in that way Second Life lacks real oceans to be explored, there are only coast lines. I would love to build a ship and sail north to the other continents but that can't be done.
The selection of water as a symbol of nothing rather than just black space is rather poetic. The vast dream ocean from which new land masses may some day emerge. But it also shows a cultural bias of SF based Linden Labs. Western civilization emerged and spread via ocean going cultures of Portugal, Spain, Holland, France, Britain and then the United States and it was via ships on the Ocean the English, the true language of Second Life, was spread. Second Life inherits the colonial legacy of the western project to explore and it makes sense that borders would be seen as water.
How would second life be different if the ends of the words were viewed as vast desserts, as an Arab might see it, or huge mountains like a Tibetan would? The vision of the world ending in an ocean would make sense to a Roman or European, but Mohammed or the Buddha would never view water in that way.
I also wonder at the lack of customisation, why can't the world have different ends. Constructing different ways the SL universe is bordered by nothing would be a lot of fun, and something more creative than just a big blue ocean can surely be done. Perhaps Second Life rests on a massive turtle, or just falls off in to a field of stars, or has a white picket fence around it guarded by devils who chase you away if you try to enter.