A specific way to map a constellation in QAM with gray code

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muboote

Newbie level 1
Good Morning

My question is: is there a specific way to map a constellation in QAM with gray code? i mean is there a rule by which we have to start the mapping for exemple the position of the first symbol and so on? if there is, is it the same for all the MQAM type? i mean 16QAM, 64QAM,...
because i saw that some constellation diagram starts from the top left most quadrant others from the botom left,...