Schematic of the observational structure of the GBTDS. Six fields toward the Galactic bulge are observed sequentially in a cycle; this is a GBTDS mosaic. During high-cadence observing seasons (the first three and last three seasons), this mosaic is observed continuously; during low-cadence observing seasons (the middle four seasons), this mosaic is observed roughly every 5 days. The filters in which this mosaic is observed are schematically shown; blue is F087, purple is F146, and red is F213. Note that the temporal axis is not drawn to scale.