As the Overground name implies, the majority of the network is above ground, and it mostly consists of railway lines that connect areas outside Central London, with a considerable portion of the network in Zone 2.
Da Overground-navnet indikerer at hovedparten af netværket er over jorden, består det mest af jernbaner, der sammen forbinder forskellige områder udenfor det centrale London, med en betydelig del af netværket i takstzone 2.