In the top right corner of the map window is an overview map which shows the extent of the main map window.
Clicking on the '+' symbol in the top right of the overview map will expand the box to show a checklist of map features that can be turned on.
Many of the layers listed have extra information about the features on the map. If a layer that can be queried for further information is currently turned on, the mouse cursor will change to show a question mark, though this will vary depending on the type and setup of the computer or device you are using to view the website.
Clicking on a queryable feature will return further information recorded about that feature in a popup box, though not all features have extra details.