Relative coordinates or NPC in ggplot2

In ggplot2 we use the coordinate system to place the element in the plot. But sometime we need to organise multiple plots or place images, and we place the element relative to a parent element, and we use a different coordinate system : “Normalized Parent Coordinates” or NPC.

Understanding text size and resolution in ggplot2

What’s complicated about size and resolution ? Have you ever tried to reproduce a plot like the first one and make minor changes on the size or resolution and end up with something like the second plot ?