The London Datastore is the open data platform of the Greater London Authority. It is a well-known example of a city-region portal, publishing data that helps understand and manage one of the world's major cities.
It offers demographic and population projections, transport and air quality data, housing and planning statistics, and the ward, borough, and statistical boundaries used to map them. Released under the UK Open Government Licence, the data is free to reuse and pairs well with national data.gov.uk datasets.