As you get closer to an object, the object appears to get smaller. This is because of the concept of perspective and the difference between apparent size and actual size. The visual angle that determines apparent size can be thought of as the angle at the top of a triangle. The eye is the top of the triangle, and the bottom of the triangle is formed by the ends of the object youre looking at. As an object gets closer, the visual angle increases, so the object appears larger. As the object moves farther away, the visual angle decreases, making the object appear smaller.

When things are closer to you, they take up more of your field of view, so they seem bigger. When theyre further away, they take up less of your field of view, and so seem smaller. For example, if you look at a building from a long way away, you can easily see the whole building from top to bottom. So the angle between the line from your eye to the top of the building, and the line from your eye to the bottom of the building, is quite small. The further away the object is, the smaller this angle will be. So, the subject appears small, because it takes up less of your field of view. But as you get closer to the building, it will take up more and more of your field of view, as the angle between the line from your eye to the top of the building, and the line from your eye to the bottom of the building, grows larger.

In summary, objects appear smaller as you get farther away from them and larger as you get closer to them due to the concept of perspective and the difference between apparent size and actual size.