Final answer:
As altitude increases, atmospheric density decreases.
Step-by-step explanation:
The relationship between altitude and atmospheric density is that as altitude increases, atmospheric density decreases. This means that the higher you go, the thinner the atmosphere becomes. In the given example, the density of the atmosphere at an altitude of 1,291 kilometers is not provided. However, based on the trend shown in the graph, the atmospheric density would be significantly lower compared to sea level.