The Survey dictionary contains classes that support ground based sky surveys. A location on the celestial sphere, consisting of right ascension and declination. The position of one corner of an image The portion of the sky contained within an image, identified by its four corners The limiting magnitude of the image The limiting magnitude of a point source at a significance of n-sigma (i.e. a S/N of n) The limiting magnitude of the image, expressed as a magnitude, and the percentage of known objects detected at that magnitude The properties of the peak of the histogram of stellar magnitudes within the image. Sky Survey related properties. This section contains the simpleTypes that provide more constraints than those at the base data type level. The simpleTypes defined here build on the base data types. This is another component of the common dictionary and therefore falls within the common namespace. The band for which the limiting magnitude specification is applicable Further classifies calibration images by the type of calibration field used. Identifies which corner of the image is being located. This assumes that the image is displayed correctly according to the orientation information provided in the display dictionary The declination component of a coordinate, decimal degrees Time that defines the origin of a celestial coordinate system, given in fractional year. Type of year may also be indicated. For example, 'J2000.0' corresponds to an origin specified by January 1, 2000 at 12:00 Terrestrial Time in Julian years. Project-dependent field ID Magnitude at which a threshold known objects are detected Represents the value of n for n-sigma limiting magnitude: The limiting magnitude of a point source at a significance of n-sigma (i.e. a S/N of n) Identifies the intent of the observation, whether it is an actual survey observation, a followup, or a calibration image. Further classifies survey observations by the technique used to acquire it. The percentage of known objects that are detected at the given magnitude for the specified band The type of observed object used to calculate the limiting magnitude The right ascension component of a coordinate, decimal degrees The full width at half maximum of stellar sources at the magnitude of the peak of the histogram of stellar magnitudes in the image, in arcseconds The magnitude of the peak of the histogram of stellar magnitudes in the image. The SNR at the magnitude of the peak of the histogram of stellar magnitudes in the image.