The 4 parts of this Hanjoku will allow you to construct a 16x16 sudoku grid (easy).
A sudoku 16x16 is presented like the union of 4 big squares, each one having 4 littler squares, each of those last ones beeing composed of 16 cells, wich can contain digits or letters.
Here are the the 4 big squares in the sudoku grid :
C1 C2
C3 C4
The Hanjoku part 1 will be the square C1, the part 2 will be the square C2 etc
A 16x16 sudoku grid uses the digits from 1 to 9 and the letters A B C D E F and G.

But as it is impossible to include a big square (above spoken) with its data in a hanjee grid, an encoding method is needed.

Each big square is composed of 64 zones, each one having 16 cells.
Each zone is then the similar of the sudoku cell in the same position.

Encoding of a zone couldn't be done with only 1 black cell in one of the 16 cells of the zone : the hanjee stayed unsolvable (too much isolated black cells, giving then too much possible solutions).
Same thing with 2, 3, 4, 5 and 6 black cells.
But with 7, encoding was possible and gives the solvability to the hanjee. And it makes also the solution unique !

How is a sudoku data encoded in a 4x4 cells zone of the hanjee grid ?
Simply ! in a zone, are two small perpendiculars (of 4 black cells each).
The junction point of these perpendiculars is a position, wich one has a value of a number or of a letter.
Here is the "value" of these junction points in a 4x4 zone :
1 2 3 4
5 6 7 8
9 A B C
D E F G
And here are some examples of junction points and what they represent: ( "Z" are black cells)
Z Z Z Z 1 2 Z 4 Z 2 3 4 1 Z 3 4 1 2 3 Z
Z 6 7 8 Z Z Z Z Z 6 7 8 5 Z 7 8 5 6 7 Z
Z A B C 9 A Z C Z A B C Z Z Z Z 9 A B Z
Z E F G D E Z G Z Z Z Z D Z F G Z Z Z Z
correspond respectively to 1 , 7 , D, A and G.

There is also a little trick to know, wich also helps to fill the grid.
When a 4x4cells zone is like this :
x x x x
x Z Z x
x Z Z x
x x x x ("Z" is black, "x" is white)
it means that there is no data in the corresponding zone of the sudoku.

Now it's time to solve the 4 hanjokus and to reconstruct the sudoku grid, wich will be easy to solve.

See you soon