The diagram depicts the part of the Earth from where the end of the transit (egress) can be seen with Venus and the Sun above the horizon. Note that the stereographic projection adopted in this diagram somewhat exaggerates the scale near the border.
The equator is drawn in black and the grid lines for longitude and latitude are drawn at 10º intervals. The red lines indicate the polar circles, the Tropic of Cancer and the Tropic of Capricorn.
The blue circles indicate the geometrical altitude (i.e. uncorrected for refraction) of Venus above the horizon at 10º intervals. The border defines the locations where Venus is on the horizon (altitude 0º), rising on the western half of the diagram and setting on the eastern half of the diagram.
The blue dot in the centre of the diagram indicates the sub-Venus point, the place where Venus is in the observer's zenith (altitude 90º) when the transit ends. Because a transit of Venus always occurs a few weeks before a summer solstice or a winter solstice, the sub-Venus point is always slightly south of the Tropic of Cancer or slightly north of the Tropic of Capricorn.