Cardiff in making iron and later steel, brought to the sea by packhorse from Merthyr Tydfil. This was first achieved by the construction of a long canal from Merthyr (510 feet above sea-level) to the Taff Estuary at Cardiff. Eventually the Taff Vale Railway replaced the canal barges and massive marshalling yards sprang up as new docks were developed in Cardiff – all prompted by the soaring worldwide demand for coal from the South Wales valleys. At its peak, Cardiff's port area, known as Tiger Bay, became the busiest port in the world and – for some time – the world's
Cardiff Urban Area almost 37% on the 2001 population of 327,706 this was mainly due to Caerphilly and Pontypridd becoming part of the built-up area. The population of the Cardiff unitary authority (not co-terminous with the built-up area or the wider urban area) in 2001 was 305,353. Cardiff Council estimated the population of the unitary authority at 317,500 in 2006, as of the 2011 census it was 346,090. According to the ONS definition the Cardiff Urban Area had the following subdivisions: Notes: Cardiff Urban Area The Cardiff Built-up Area or Cardiff Urban Area is the name given to the urban area around Cardiff.