@Nailik. Gravitational pull of an object decreases as one over the square of the distance from the object. But it also increases with more mass. This means that Gwen's sense of mass (and more importantly its shape) becomes more clear as she gets closer to it. And the larger a mass is, the farther away she can sense it. Since it's a tower with lots of stuff in it, without her trance state, a lot of stuff is very blurry, but she has an approximate sense of how much mass there is already. With her trance state, a lot of stuff is in there that becomes less blurry. But since it's very far away, I guess it would be more clear as to the amounts of mass that are moving and a rough shape as to what they look like.