Question

1) islands:groups of islands have plural names with "the".The British isles
2) but an individual island doesn't take "the"
3) cities: the names of cities,towns.villages do not have"the"

Answer 1

1 The Philippines,  The Bahamas, The Canaries, The Bermudas
2 Madagascar, Kalimantan, Sakhalin, 
3 Moscow, Kapetown, Odessa, Tomsk.......................