City of London different from London
Geography
The City of London is the smallest ceremonial county of England by area and population, and the fourth most densely populated. Of the 326 English districts, it is the second smallest by population, after the Isles of Scilly, and the smallest by area. It is also the smallest English city by population (and in Britain, only two cities in Wales are smaller), and the smallest in the UK by area.
The elevation of the City ranges from sea level at the Thames to 21.6 metres (71 ft) at the junction of High Holborn and Chancery Lane. Two small but notable hills are within the historic core, Ludgate Hill to the west and Cornhill to the east. Between them ran the Walbrook, one of the many "lost" rivers or streams of London (another is the Fleet).