Know Your Place
The Know Your Place Website is a fascinating and interactive way to compare old and new maps. Select your maps and drag the slider to compare.
The key at the right allows you to select various markup options, such as the Gloucester Historic Environment (HER) layers or Industrial Archaeology from the Gloucestershire Society for Industrial Archaeology (GSIA)
Rather than explain it, it is best to have a go! https://maps.bristol.gov.uk/kyp/?edition=glos