Click on the image to view the “image” in high resolution. Since it is actually a vector, not a rasterized image, you can zoom in as much as you want.
The numbers inside the dots represent the lap in which that particular time was done. Drivers who did their laps later in the session will tend to have faster times. Keep that in mind when comparing the lap times done by different drivers.
Note: Grosjean only did 2 laps that could be more or less considered as race pace simulation. Kvyat and Magnussen are on the same boat, doing only 3 race simulation laps. Their numbers are not necessarily representative of their actual race pace.