Those results are a bit weird cos from that test it looks like the multidimensional array is faster. I think this is because it takes time for Flash to evaluate map2[0*w+j] for the flat array.
Also, I downloaded your Flash 9 source (which is AS2 by the way) and modified it for AS3 and it still looks like the multidimensional array was faster.
Even more argument to use multidimensional then...
Also, I downloaded your Flash 9 source (which is AS2 by the way) and modified it for AS3 and it still looks like the multidimensional array was faster.
Yes, in AS3 accessing multidimensional array is much faster then flat array with width.