When using a compass anywhere in the world, you should know the declination of the area you are located. The compass will always point toward the magnetic but true north can vary, this difference is called the declination. Declination is caused because the magnetic north is controlled by the liquid iron core of the earth which moves by sometimes miles each year.
As a result the magnetic north moves constantly, while the true north is forever fixed. So remember that when looking at a map, it is draw to the true north, while you compass will point toward the magnetic north.
These are some documents that may help.