Why does inner London not have definitive maps already?
This is really due to a historical anomaly. When definitive maps were put into effect by the National Parks and Access to the Countryside Act in 1949, focus was on rural paths. However, over time, the value of urban footpaths for exercise and recreational activity became recognised, and the Ramblers began to lobby for definitive maps to be extended to large towns. The lobbying was successful and the Wildlife and Countryside Act 1981 extended definitive maps to all areas, except inner London.