CONGRATULATIONS ZERO BAHAMUT!! the answer is MIDGAR!.
though body is seperated under one (8 sectors make up midgar)
my heart stands tall towards the sun (the shinra HQ that towers aboe everything else, and the heart of shinra)
my power glows all way round (the ring of 8 mako reactors)
though the greatest lies nearest the ground (aeris with the white materia in the sector 5 slums church below the 'plate')
Well Done Zero Bahamut! Riddle away my friend...