The data shown here comes from Boston Crimes Dataset
This chart meant to show the "Major Crimes in Boston". The color denotes the number of occurrences of that crime in that particular year. The drop down allows you to choose the year for which you would like to see Crime Count.
The inspiration for this drop down menu was from https://vizhub.com/pichayutter/88497edd1bcb466997c8d73dc10bf35d