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.
This mechanism is more efficient than a fixed route that visits all nodes in order, and also allows easy cross-zone farming.
The add-on is configurable in the Interface menu under Add-ons / Bloodhound. It allows you to select whether the cross-zone feature is enabled Never, While Flying, or Always. It lists the zones in the current continent and lets you select which zones to include for the cross-zone feature. If that's disabled, it ignores nodes outside the current zone. It also lists the herbs and ore available on the current continent and lets you select the one's you're interested it. Unchecked node types don't exert any pull or show any indicator on the mini-map.