How does vapor pressure affect the volume?
Volume does not affect vapor pressure !
The liquid in a container is in equilibrium with the vapor. When the volume is changed, for example - decreased, some of the vapor in the container turns into it's liquid state. Furthermore, if the volume is increased, some of the liquid will change into it's vapor state.
Why does this occur? So that the pressure can remain constant.
A video to drive home the concept (recommended to watch!):
Does Vapor Pressure Increase With the Increasing Volume of the Liquid? : Chemistry Lessons
Published on Feb 7, 2014
Expert: Robin Higgins
Filmmaker: Bjorn Wilde