There are ways to estimate HR zones including the formula 220-age to find out maximum heart rate. Zone 2 is approximately 60-70% of maximum heart rate. For me, HRmax would be 220-30= 190.
A Travelcard gives you unlimited travel within London zones 1-4 or 1-6 on the Underground, Overground, TfL Rail, Docklands Light Railway, buses, trams, and most National Rail services in London*.
High Street Kensington is a London Underground station on Kensington High Street, in Kensington. The station is on the Circle line between Gloucester Road and Notting Hill Gate, and the District line between Earl's Court and Notting Hill Gate and is in Travelcard Zone 1.
Shoreditch High Street station on the London Overground line* is a Zone 1 station that sits between two Zone 2 stations, Hoxton and Whitechapel. It is the only station on the entire line that sits in Zone 1. The rest of the stations on the Overground line sit in Zones 2, 3, 4 and 5.
On the District line and Circle line, it is between High Street Kensington and Bayswater stations. It is on the boundary of Travelcard Zone 1 and Zone 2.
But Zone 2 in East London and South London has some relatively high crime areas, and a significant number of people living in social housing. The best Zone 2 areas are in North London along the Hampstead branch of the Northern Line underground, and the Jubilee line going through St. John's Wood.
Zone 1 is considered the target range for warm-up and recovery work and should be about 50-60% of your heart rate (HR) max. Zone 2 is considered the target range for aerobic and base fitness work and should be about 60-70% of your HRmax.