The relationship between the change in density with a change in depth. In many areas of the world with thick clastic sections the increase in density with an increase in depth has been shown to be primarily a function of compaction. However, age, lithology and porosity may also influence the relationship. The relationship is important in gravity modeling because a gravity anomaly may be caused by a gradational change in density rather than a relatively abrupt density contrast, such as that which may occur at a fault, contact, or unconformity.