They key concept in drawing in perspective is the vanishing point: every line in your slide should disappear in it (see an earlier blog post). It turns out I got the concept slightly wrong all the time. Because of the curve in the Earth’s surface, the real vanishing point for someone standing at sea level is actually below the horizon. A vanishing point that sits on the horizon, would require the radius of the Earth to be 64x as large. (For comparison, the Sun as a radius about 109x that of Earth.