keeptrack.space was mentioned in What would be a “big picture” understanding of how the orbits of Earth satellites are monitored? but I haven't visited the site since.
Running across this again today I noticed there seems to be several additional features. I lack a video game mentality and so baffled by the GUI-driven site, but I noticed the option
Set/Hide Surveillance Fence. Clicking it generated a message to select a sensor so I chose
CSpOC Sensors. I clicked
Set/Hide Surveillance Fence again but nothing happens.
Question: What does the Surveillance Fence feature do? How can one use and make use of it?