Examples of field data include the physical size of a settlement, and how it grows over time, and the appearance, or disappearance, of settlements. For example, after the Black Death the archaeological record shows the abandonment of upwards of 25% of all villages in Spain. However, archaeological data are often difficult to interpret. It is often difficult to assign a precise age to discoveries. Also, some of the largest and most important sites are still occupied and cannot be investigated. Available archaeological records may be concentrated on the more peripheral regions, for example early Middle Ages Anglo–Saxon burials at Sutton Hoo, in East Anglia in England, for which otherwise no records exist.