The collection of archaeological finds from disturbed ground surfaces (e.g. cultivated fields) with the objective of gathering representative samples in order to establish the types of activity within the area examined. Such surveys may be unsystematic: that is, the pattern of scanning is unstructured and simply involves scanning the route of a more or less precisely defined path. By contrast, systematic surface survey involves setting out a grid across the survey area and either walking each line as a series of stints of defined length and duration (line walking), or spending a set amount of time scanning the surface of each grid square (grid recovery). The material collected during surface surveys can be quantified under a series of classifications, and trend surface analysis can be used to produce density plots for particular classes of material (flint tools, Roman pottery, etc.).