I dont blog every density design visual even though it is tempting, as they are so clear and beautiful. But this one i had to, another excellant visual. always like julien bayle says, clear, clean, simplfied complexity and the bold colours just draw you into closer inspection, had to look it in the largest size for 'all sizes'.
would say the lines arent so easy to follow for the population at bottom, but dont strictly need to follow the individual lines and adds beautiful texture to contrast the bold colours.
i'm sure the lines have levels of solidarity too them also for further info of importance/density.