Where is heaven?

Since visiting great grandma's grave in Shanghai last year, N and I have had on and off conversations about death and what happens when people die.  He's asked some interesting questions like where people do after they die, and how long will it be until I die.  Very hard questions to answer!  I said that some people believe there's a heaven.  That brought a lot of comfort to N since he said "after you die, I'll come and find you in heaven".  I pointed out that nobody knows where heaven is, so it'll be very hard to find.  He replied, "that's okay, I will type it into the GPS!"