Image credit: Cyp
Views of spacetime along the world line of a rapidly accelerating observer (see Lorentz transformation).
Vertical direction indicates time. Horizontal indicates distance, the dashed line is the spacetime trajectory ("world line") of the observer. The lower quarter of the diagram shows the events visible to the observer. Upper quarter shows the light cone- those that will be able to see the observer. The small dots are arbitrary events in spacetime.
The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. Note how the view of spacetime changes when the observer accelerates.