Explanation for Jelly Program to make Cityscape (Erik)

Œgx'2z⁶ṚY  Main Link
Œg         Group runs of equal elements
  x        Repeat
   '              each individual list
    2                                  twice
     z⁶    Zip (transpose), filling in blanks with spaces
       Ṛ   Reverse the whole thing so it's upside-down
        Y  Join by newlines