The rationale behind a survey is that it would reveal the characteristics of those standing for election and those who get elected to local government at the normal elections (not by-elections).
Y rhesymeg y tu ôl i gynnal arolwg yw y byddai’n datgelu nodweddion y rhai sy’n ymgeisio a’r rhai sy’n cael eu hethol ar gyfer llywodraeth leol mewn etholiadau arferol (nid is-etholiadau).