These are called non-invasive techniques, as they do not involve the destruction of the site. Often 'evaluation' is required to locate the most promising areas of a site to target during a full-scale excavation. Rescue excavations have to be finished as quickly as possible, so the topsoil and overburden is generally stripped using a mechanical excavator. On rural sites, the soil is taken off to the natural subsoil. Archaeological features usually show up very clearly as darker or lighter patches.
Urban sites are more complex owing to the continued reuse of the land over many generations.
After stripping, the site is cleaned using hoes or shovels to produce an even surface in which features can be seen. These are then hand-excavated using a combination of mattocks, shovels and trowels. Experience is the key to deciding which tool is the most appropriate for the job. The actual excavation technique chosen depends on the type of feature. Pits and postholes are usually half-sectioned, after which the remaining half is drawn and photographed.