Guild Wars 2

How come fps is really high in some places and really low in others in the world ?

I comes down to the amount of stuff on screen.
Generally speaking, the further you can see and the amount of scenery objects on screen causes a reduction in framerate. It takes more power to render more.

There’s also something that other engines have suffered from in the past. I’m not privy to how GW2’s engine works, so this is pure conjecture, but maps in other games have suffered “memory leaks” from badly constructed level geometry. This gradually results in lower and lower framerates, until you either load another map or restart the game.

I doubt this happens so much in GW2 though, as I believe it relies heavily on “Streaming” of level geometry.

This is where the game is continuously loading stuff in the level into memory in an attempt to predict where you’re going next and have it ready for when you get there; think of it like a bubble whose borders extend just beyond your current visible horizon.
I’m 99% certain GW2 uses this technique, as a dead giveaway is that you have longer loading screens the further away you waypoint in the same map.
If you teleport to a waypoint that’s within sight, the load screen will be minimal, almost instant on SSD.
However, a waypoint further away and out of sight resides in an area not rendered by your streaming bubble, so the game has to create a new streaming bubble for you centred on that waypoint.

I hope that helps explain things.
And feel free to step in and correct me any game developer types with a better working knowledge of these things.

Addendum:
Also, things like particle and smoke effects are VERY expensive to render as well.
One excellent predictable example of drastic frame drop is when the Fire Elemental spawns in Metrica Province. He appears in an explosion of flame and smoke, and your machine will likely grind to almost a halt as it tries to catch up with the effects being rendered.

Interestingly, snow, while having a marginally noticeable impact, doesn’t seem to be as drastic as smoke and flame.
I’m guessing this is because it’s more of a full scene effect with minimal physics modelling happening, whereas smoke, fire and fog in this game seem to have a degree of fluid physics going on.

Thanks for the information.

Appreciated.