You will find a picture of a larger house (top left), a fortress (bottom right), a flag (top right) and a smaller house (bottom left).
The big compass rose is pointed as follows:
top left = north
top right = east
bottom right = south
bottom left = west
If you have both the large and small compass rose properly aligned, you will get the following letter combination with which you can solve the codes:
top left: A=E
top right: A=V
bottom right: A=P
bottom left: A=i
The 4 decrypted lines read:
top left: this island is not on roman numerals 3 or 4
top right: this island is on roman numerals 2 or 3 or 4
bottom right: this island is not on roman numerals 2 or 4
bottom left: this island is on roman numeral 1
You have to combine this solution with the puzzle of the 4 ships.
for the hints that combine this puzzle with the puzzle with the 4 ships.