Greater London South (Victoria-St. Mary Cray)
Outside immediate London area, maps are generally grouped by counties, some of which are historically known as "shires".
Kent West (Swanley-Gillingham)
Kent Central (Gillingham-Faversham)
Kent East (Faversham-Dover)
The London area has a dense railway network, all part of the same system. Which has enabled the creation of numerous connecting lines between the various main lines. These connecting lines increase the availability of travel options. Which include the possibility of alternate routes in and out of London, including terminating at different main stations.
Most lines are shown on zoomable Google Maps.