That whole saṃyutta is a good place to look.. The sutta right after, SN 15.6 (Sāsapa Sutta), has another great analogy:"Monk, in a poor city there is a block of mustard seeds seven miles by the length, breath and the height bound together by the roots. After the lapse of one hundred years a man comes and takes out one of the seeds. By this method the mustard seeds diminish and vanish but the world cycle does not come to an end"http://tipitaka.wikia.com/wiki/Sasapa_Sutta
The yojana is translated as seven miles in this..
Out of curiosity, where did you get that definition for the yojana - do you have some sutta source?