Treasure Map Drawing Bot
J, 37 34 bytes

0&lt;@|:' x'{~((i.@]e.#.~)1+&gt;./) ::#:


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                       1+&gt;./          maximum for each coordinate + 1
             i.@]                     make an array with these dimensions filled with 0..x*y
                                      /* if the input is empty, 
                                         1+&gt;./ is negative infinity
                                         and i.@] throws an error  */
                   #.~                mixed base conversion of input
                 e.                   replace the elements of i.@]
                                        with 1 if it's present in the
                                        converted input, 0 otherwise
           (                ) ::      if there's an error do the other thing instead
                                #:    "to binary", for empty input this returns a 0x0 matrix
0&lt;@|:' x'{~                           index into character string, transpose and put in a box