Indonesia does extend exactly 30° along equator, just as everyone can see on a map (approximately from 99°E to 129°E). It fits to the analysis that underneath there is a convection roll in the lower mantle, exactly 30° wide. This is the big mystery of the equator line!
Looking at the details of Indonesia, some interesting forms show up. Two of the convection division lines look like this:
With these calculated lines put into place, let us look at how nature has shaped the tectonics around:
This is a place of symmetry, and square forms! A more detailed analysis can tell us much more.