Alignment.

 It is difficult to show the baseboard alignment method I use. Basically a male fits a female - brass turnings which fit into 8mm holes drilled in the ends of boards which have been clamped together hopefully in the right position!
The snug fit makes sure that the boards fit in the right place every time.
Moving to fiddleyard tracks being held in the correct place- I use square brass tube with a solid square bar which fits snugly.
Bent at the end and used as a simple bolt which makes each trach align with its intended route.

The bolt also gives electrical connection to the intended route.