What is considered a land of Islam?

What is Dar al Islam (a land of Islam)? This is an important matter. Dar al Islam is a place where the symbols of Islam are shown open in public, like the Adhan (call to prayer), establishment of the Friday prayer, and the congregational prayer. And it is known that it is a land of Islam, even if the rulers don't rule by Islam, because the principle is by what is apparent. So, as long as what is apparent in the land is Islam then it is considered Dar al Islam. As for a land that does not rule by Islam, and the symbols of Islam are not made apparent, and it's people are prevented from calling the Adhan with a raised voice, and from establishing the congregational prayers, and from establishing the Friday prayers, then this is Dar al Kufr (land of disbelief).