Connecting together modular layouts


I'm about 1/2 way through my first "practice" layout (1'x6'). I'm sticking with modular / shelf type layouts until I can take over the basement (wife says 8 more years :) ... Plus I like the concept of building small sections that are detachable and portable in case I move. I've done much better then I expected with this layout so am considering instead of donating it to the trash man, actually incorporating it into a larger layout.
This means I'll make a new section someday (maybe 1.5' x 6' ) and try to "hook them together". Thats the part I am having problems with. I think I can figure out the electrical part, thats prety easy. I studied the NTRAX specs but they seem very complex and I didnt stick with them. What concerns me is I have 2 lines coming out each end of the layout. I may want to terminate some of them but atleast one on each end I want to 'hook onto' the next segment.
How to do that ? Physically I know I can simply clamp them together but how to arrange so that the tracks line up so perfectly that locos can go from one module to the next. Is it a matter if perfect engineering ? That is, building the next module so that the track *exactly* lines up with this one ? in all 3 dimensions ? Or is there some "trick" I can use to adjust things that are not quite right, like some kind of flexable "bridge" to compensate for imperfect layouts. Even if the tracks line-up how do I make sure there are no big gaps ? Do the tracks have to go exactly to the edge of the layout so they can match with each other or is there some other way of joining them ?

What do people do ? This seems like a common problem so maybe there's an easy solution. Or maybe its as hard as I think and you just have to be 100% perfect ...

Suggestions welcome !
This has been discussed quite a bit - you can find threads here or Google "module connectors" or similar.

Some people use wooden dowels as alignment pins, some use sash locks, some use metal pins, some use carriage bolts. I'm sure other folks here will give you a much more extensive list.

Some people achieve such good alignment that the tracks just line up, others use small lengths of sectional track to bridge the gaps.
First, you are going to have to be nearly 100% right with your measurements. Then when you want to connect them together just use a short section of flex track to bridge the gap and fix any imperfection with alignment.