Soil chemistry is especially useful in archaeology because it reveals parts of the archaeological record that are difficult to identify and interpret through excavation or geophysical prospection methods. For example, manured fields or areas used for cleaning and butchering fish and animals might only be revealed through chemical methods. Soil chemistry is used for several purposes in archaeology: site prospection, investigating settlement patterning, analysis and interpretation of archaeological features, and reconstructing activity areas and soilscapes. For these purposes, field methods can be roughly divided into two groups: prospection survey and feature analyses. In survey, samples are taken at regular intervals, and this can be done at many different spatial scales. Survey work is not dependent on known site boundaries. For feature analysis, samples or in situ measurements are taken from known contexts, generally during excavation.