sparky is correct.
Any data from any node on the RF network, will generate a new UI node automatically and add any recognized metrics (as defined in metrics.js) to that node. RSSI is automatically logged regardless, if you are using the correct RFM69 PiGateway example sketch.
Also note that the settings page has a keepMetricLogsOnDelete setting, if that is false, whenever you delete a node, it also deletes any logged data for that node, otherwise it keeps the data and only deletes the node from the UI.