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.
The box represents the interquartile ranges (IQRs), with the lower bound representing the 25% IQR and the top bound representing the 75% IQR. The horizontal line represents the median time, which is also displayed in the colored label above each driver. The whiskers represent the minimum or maximum IQR +/- 1.5*IQR. This basically means that laps above or below the whiskers are considered as outliers.