‘Layers’ are information related to the registered activities that can be displayed on the 'Map'. Each 'Theme' has a list of specific ‘Layers’ for viewing which can be selected together or individually. 
In order to enable it, just check the desired box and then click on  again.
Each Theme has a specific set of layers that can be enabled. The following links contain all Harvest and Spray themes.

Harvest Harvest Shaker Rolls System Events and Stops Time Range Productivity Speed

Spray Events and Stops Time Range Overlapping Speed Applied Volume