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\begin{itemize}  \item \textbf{Scope} The first requirements for the survey concern the scope of the observations. ZTF must survey the entire sky visible from Palomar Observatory. In practice, this will cover nearly the entire footprint of the Pan-STARRS1 (PS1) 3$\pi$ survey. To enable the search for transients, it is essential that the full survey area be observed and reference images be created within the first year of the survey. Furthermore, a systematic grid of discrete fields should be developed prior to the start of the survey, and all observations should be confined to these fields. This will ensure that, once reference images are made, every frame taken by ZTF will be suitable for transient discovery. We recommend that the fields consist of two overlapping grids, offset by $\sim$half the length of the diagonal such that chip gaps can be filled and the corners of the FOV in one grid, which suffer the most from vignetting, correspond to the center of the FOV in the alternate grid. Alternative solutions may be appropriate, but they must be defined prior to the start of the survey.     \textbf{Filter Set}     \begin{deluxetable}{rrrr}  \tabletypesize{\small}  \tablecolumns{4}  % \tablewidth{240pt}  % \setlength{\tabcolsep}{6pt}  \tablecaption{ZTF Filter Requirements\label{tbl:ztf_filters}}  \tablehead{\colhead{Quantity} & \colhead{Design Spec} &   \colhead{Minimum Spec} & \colhead{Stretch Goal} }  \startdata   Imaging Filters & $gr$ & $gr$ & $gri$  \enddata  % \tablecomments{}  % \tablenotetext{a}{}  \end{DeluxeTable}  \item \textbf{Absolute Photometric Calibration} Many of the ``bread and butter'' science goals of ZTF require a precise and accurate absolute photometric calibration (e.g., cosmography with Type Ia SNe, mapping Galactic structure with RRL). Recently, PS1 has demonstrated the ability to produce an absolute calibration, relative to the Sloan Digital Sky Survey and \textit{Hubble Space Telescope} Calspec stars of $\sim$30 mmag \citep{Tonry_2012}.  PTF achived 20\,mmag scatter compared with the SDSS. However, since PTF observed mostly in a single filter, one need to know the star color in order to achive the this accuracy.  The first requirment is that ZTF will observe the sky in at least two bands.