Final Fantasy - Different countries, timelines, or universes?

In all of the Final Fantasy Games, there are many similarities:

• Chocobo (Since FF2)
• Spells like "Holy", "Meteor", and "Ultima"
• Excalibur and Masamune
• Summons - Bahamut, Ifrit and Shiva being the most common recurring ones.

Obviously, some of these Themes are a bit ambiguous - any fantasy game deals with magic and summoning, and Excalibur are used throughout any Fantasy medium. However, these recurring themes have been in (almost) every single Final Fantasy game to date.

So is there any kind of ties between the games? Whether they simply exist in the same timeline, however far apart, or are just alternate versions of the same universe?

Most Final Fantasy games take place in different worlds. The exceptions are:

• Planet AKA Gaia
  • Final Fantasy VII
  • Before Crisis: Final Fantasy VII
  • Crisis Core: Final Fantasy VII
  • Dirge of Cerebus: Final Fantasy VII
  • Last Order: Final Fantasy VII
  • Final Fantasy VII: Advent Children
• Ivalice
  • Final Fantasy Tactics
  • Final Fantasy Tactics Advance
  • Final Fantasy Tactics A2
  • Vagrant Story
  • Final Fantasy XII
• Spira
  • Final Fantasy X
  • Final Fantasy X-2
• Gran Pulse
  • Final Fantasy XIII
  • Final Fantasy XIII-2
  • Lightning Returns: Final Fantasy XIII
• "Earth"
  • Final Fantasy IV
  • Final Fantasy IV -Interlude-
  • Final Fantasy IV: The After Years

The various Dissidia games also take place in a bunch of locations from previous games.