Complex sentence: A significent number of people from Gilgit-Baltistan are resident in other parts of Pakistan, consisting of around one million, out of which at least 400,000 are in Karachi.
Split into simpler sentences: A significent number of people from Gilgit-Baltistan are resident in other parts of Pakistan. They number around one million, of which at least 400,000 are resident in Karachi.