It depends entirely how high your vantage point is.

Let's assume we are talking about a perfectly smooth, spherical globe.

If your eye is exactly at ground level, your horizon is zero distance from you. - you can look only along a tangent to where your eye is.

If you raise your viewpoint, your horizon will be a circle which is the locus of all tangents from your eye to the sphere. The higher, the bigger. Climb to the crow's nest Jim lad and see if you can see Treasure Island.

If you are talking about the effect on land - then the surface is not smooth - and the geometry gets more complicated but it's the same principle.