Geophysical Archaeology (also known as Archaeological Prospection) uses instruments such as ground-penetrating radar, magnetometry, resistivity, and conductivity to record information about below ground features without or before excavating. Geophysical archaeology data are often gathered using a grid system of survey units 20 m x 20 m with some recent advances using RTK-DGPS to rapidly collect data using RTVs to tow the instruments across the site. The instruments are moved along a transect (a straight line) while taking a reading every 2 cm or so. After reaching the end of the transect line the instrument is turned around and moved over 5 cm, 10 cm, 25 cm, or 50 cm and data are then collected while travelling back along this new line. Due to the dense sampling of data post-acquisition plots can reveal details about information of interest below the ground. Building foundations, road and walkways, storage pits, human graves, and locations where people had fires are just a few of the human-made sub-surface features that geophysical archaeology can identify.