The Principal facts of processed field observations consist of the Observed gravity value, the Latitude, the Longitude, and the Elevation. These values and the elevation estimates for adjacent areas for calculation of inner zone terrain corrections are used to calculate various gravity anomaly values. Data that comes from a special gravimeter placed at a base station. Elevation is a Principal fact. The Principal facts of processed field observations consist of the Observed gravity value, the Latitude, the Longitude, and the Elevation. These values and the elevation estimates for adjacent areas for calculation of inner zone terrain corrections are used to calculate various gravity anomaly values. A rectangular array of numbers or values (a geospatial matrix of sorts in which each value is a constant distance from the others ). Raw gravity readings are taken at irregular intervals on the Earth's surface because we cannot gather data in a perfect grid in the real world because of rivers, mountains, military bases, etc. Usually we have to follow roads. Contouring to maps maps and filtering require values that are arranged in a perfect array or grid. Thus, the anomaly values of interest are extracted and interpolated onto a regular grid. Mathematical methods that remove the long wavelength anomalies leaving the local (short wavelength) anomalies behind. Mathematical methods that attempt to break the anomaly field into regional and local (residual) components. Latitude is a Principal fact. The Principal facts of processed field observations consist of the Observed gravity value, the Latitude, the Longitude, and the Elevation. These values and the elevation estimates for adjacent areas for calculation of inner zone terrain corrections are used to calculate various gravity anomaly values. Longitude is a Principal fact. The Principal facts of processed field observations consist of the Observed gravity value, the Latitude, the Longitude, and the Elevation. These values and the elevation estimates for adjacent areas for calculation of inner zone terrain corrections are used to calculate various gravity anomaly values. The Observed gravity value is a Principal fact. The Principal facts of processed field observations consist of the Observed gravity value, the Latitude, the Longitude, and the Elevation. These values and the elevation estimates for adjacent areas for calculation of inner zone terrain corrections are used to calculate various gravity anomaly values. Observed Gravity Values that have had corrections performed on it such as Bouguer, Free Air, Latitude, etc. By reading a gravimeter at base station and then at a particular gravity station, we can convert the difference into an Observed Gravity Value by correcting the readings for earth tides and meter drift.