If you have Find Herbs or Find Ore switched on, this add-on displays a red arrow on the minimap. Follow it and it will lead you to herb/ore nodes. Potential node locations show as red gems on the minimap. They're transparent so that you can see actual nodes.
The arrow points in the direction of "net pull" exerted by the nodes. The longer you go without visiting a node, the stronger it pulls. Once you visit it, the pull drops back to zero and the arrow points somewhere else. This will eventually lead you everywhere, but it's a dynamically updating system, responding to where you go automatically. Closer nodes pull more strongly, so it favors nearby clusters of nodes. If you choose to ignore the arrow and go somewhere else, the arrow will adjust to your new location which means you're not on a fixed track.