chronology that describes a period of human or protohuman prehistory. Some archaeological timescales are based on relative dating techniques, such as stratigraphy, which illuminate a sequence of change. Others are based on chronometric (absolute) methods such as carbon-14 dating and dendrochronology that derive a specific date from a specific item or sample (as of carbon). Most also include geographic information, as change generally varies over space as well as time. The scales of time and space considered vary depending upon the purpose of the archaeological chronology: a timescale describing the development of a locale from prehistoric campsite to medieval village to modern town might be measured in centuries and spatially restricted to a few acres or hectares, while one describing human evolution would be measured in millennia and would consider space at the level of the ecosystem or continent.