Given this paragraph, in what part of England does the River Thames flow, and what is its length in kilometres?

Context: The River Thames, known alternatively in parts as the River Isis, is a river that flows through southern England including London. At 215 miles, it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn. The river rises at Thames Head in Gloucestershire and flows into the North Sea near Tilbury, Essex and Gravesend, Kent, via the Thames Estuary. From the west it flows through Oxford, Reading, Henley-on-Thames and Windsor. The Thames also drains the whole of Greater London.

Answer: The River Thames flows through Southern England and it is 346 kilometres long.