Historic England information for Yarnbury Henge:
https://historicengland.org.uk/listing/the-list/list-entry/1008877
Historic England information for Multi-period lead mines and processing works and 20th century barytes mill
https://historicengland.org.uk/listing/the-list/list-entry/1018333
Model: DSM LIDAR 0.25m Methodology at: https://www.eastmead.com/QGIS-LIDAR.htm