A pin's brightness shows how recently that location last listened, over the whole period shown at the top.
Bright, solid — heard just now, or very lately.
Faint, ghostly — not heard for a long time.
Everything in between scales smoothly. Click any pin for when it was first and last heard, per channel.
Why not how long? A stream stays connected even when the teletype beside it is switched off, so connection time does not measure listening — and it means something different on the always-on channels than it does on AUTOSTART.
Very brief connections are left out altogether. Automated clients probe the streams around the clock, connecting for a few minutes and dropping, each from a different place; counted, they would fill the map with locations nobody ever listened from. A connection has to last at least 5 minutes on the always-on channels, or 15 minutes on AUTOSTART, to earn a pin. The difference is deliberate: AUTOSTART is meant to be left connected waiting for an article, so a brief visit there is a probe, while dipping into the news feeds for a few minutes is ordinary listening. That is a floor for counting, not a scale for shading.