& btmapterr()
 
  Syntax: btmapterr(<MapDB>,<x>,<y>)
 
  This function returns a one-character string that represents the 
  terrain in the specified hex on the specified map.
 
  Possible output:
  .   Clear       #   Road       ~   Water
  @   Building    =   Wall       -   Ice
  ^   Mountain    }   Desert     &   Fire
  %   Rough
 
 Error Messages:
 * If <MapDB> is not valid the function will return #-1
 * If <x> <y> are not numeric the function will return #-2
 * If <x> <y> are outside the boundaries of the map the function 
   will return ? 
 
  Example: 
  Given that #62 is a map of 50 x 50
  > think btmapterr(#62,5,9)
  .
  > think btmapterr(#62,10,10)
  #
  > think btmapterr(#62,10,60)
  ?