Heres 16 maps arranged starting from the SouthEastern most one. Thats relatively simply.
0003/0103/0203/0303
0002/0102/0202/0302
0001/0101/0201/0301
0000/0100/0200/0300
And now, getting a bit more complicated... Youve got you 16 maps and you think 'I want to have a path coming off to the west DUM DA DUUMMMM!!! Well...
0c03/0b03/0a03/0003/0103/0203/0303
0c02/0b02/0a02/0002/0102/0202/0302
0c01/0b01/0a01/0001/0101/0201/0301
0c00/0b00/0a00/0000/0100/0200/0300
That should help you to visualise the process. If you have extremeties though, and your paths wind their way northwest and south, there wont actually be a most southwestern map. So you have to 'imagine' that there is one to be named - in this senario - map_0f0d and then you will end up with...
0f03/----/----/----/0c03/0b03/0a03/0003/0103/0203/0303
0f02/----/----/----/0c02/0b02/0a02/0002/0102/0202/0302
0f01/0e01/0d01/0c01/0b01/0a01/0001/0101/0201/0301
/----/----/----/----/0c00/0b00/0a00/0000/0100/0200/0300
/----/----/----/----/0c0a/----/----/----/----/----/----/----/----/
/----/----/----/----/0c0b/----/----/----/----/----/----/----/----/
/----/----/----/----/0c0c/----/----/----/----/----/----/----/----/
/---/---/---/0d0d/0c0d/----/----/----/----/----/----/----/
The /----/ are simply areas on the grid with no maps attached.
Thats about as simple and big as the whole thing really is, but as many people have said: Draw out your maps onto paper first, then you know at a glance which map goes where.
Have fun

EDIT: Thanks Grom, I got carried away you're right -- Fixed