This involves mapping the energy signatures of ships as they enter and exit hyperspace. Darth Vader tracked the Tantive IV in the first Star Wars film with a faulty hyperdrive, which Lucasfilm's Star Wars: The Rise of Skywalker visual dictionary confirmed. Before the Death Star destroyed Scarif, agents of the Acolytes of the Beyond stole some of the technology and were able to use it.
The First Order might have been able to use hyperspace routes the New Republic didn't know about if Supreme Leader Snoke had restored it before the sequel trilogy. The First Order destroyed the New Republic in Star Wars: The Last Jedi. Had she remembered how Darth Vader pursued her to Tatooine, she could have figured out how to adjust her ships' hyperdrive signatures so the Resistance could escape.
The Imperial navigation network was not maintained after the Battle of Jakku. The Imperial navigation beacon were fitted with extensive sensors to monitor background levels of radiation, which could be used to facilitate hyperspace tracking. The Empire had been working on this technology on the planet Scarif, according to an Easter egg in the movie. After the Battle of Yavin IV, her young mind was preoccupied with so many different thoughts that she forgot this. It's possible that the Tantive IV was sabotaged because the Organas were connected to various rebel cells.
There is a degree of irony in the fact that hyperspace tracking was used. When the First Order wanted to capture Leia's flagship, hyperspace tracking would be a very useful benefit. Hyperspace tracking is seen in Star Wars: The Last Jedi.
Shadow of the Sith explains how hyperdrive tracking works.
Hyperspace tracking was the key to the First Order's success. The Resistance came close to destruction over the next few days. The Resistance's greatest hour should have been the destruction of Starkiller Base. The forces pressed in on the Resistance, forcing them to flee to an abandoned Rebel Alliance base. It is possible that Star Wars: The Last Jedi could have turned out differently.
Darth Vader probably used an early version of this technology to track the Tantive IV's hyperdrive emissions. The technique is known as hyperwave signal intercepting.