An area to be surveyed by the gravity method is covered by a pattern of intersecting traverses along which gravity values are measured. The spacing between observation points depends on the detail required, but is generally half a mile to a mile. After the observed gravity values have been corrected for the effects of latitude, elevation and topography they are plotted on a map and contoured to show variations in the earth's gravity field. The interpretation of gravity data involves assumptions of the structural shapes and density contrasts in the subsurface rocks to great depths. As knowledge of these factors is generally limited, particularly at the reconnaissance stage of an exploration programme, interpretation of gravity data is likely to be ambiguous and should only be used to provide leads for further geophysical exploration.