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\subsection{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}     An important lesson from PTF is that the survey itself must provide color information, if this is to be utilized in near-real time. While there are many $\sim$1-m class telescopes suitable for photometric follow-up of ZTF discoveries, unlike ZTF, these telescopes will in almost all cases lack reference images. Thus, with the exception of variable stars and ``hostless'' transients, these telescopes will need to wait for the transient to completely fade before obtaining the appropriate reference images for image subtraction. Thus, it is viewed as a requirement that ZTF, unlike PTF/iPTF, have at least 2 photometric filters in order to produce color information in quasi-real time.     \textit{Specification}: the filters for ZTF are specified in Table~\ref{tbl:ztf_filters}.    % \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}  \begin{table}  \begin{tabular}{ rrrr }  Quantity & Design Spec & Minimum Spec & Stretch Goal \\   ZTF filters & $gr$ & $gr$ & $gri$ \\   \end{tabular}   \caption{\label{tbl:ztf_filters} The photometric filters for ZTF}  \end{table}  The baseline design includes only the $g$ and $r$ filters as these correspond to the lowest sky backgrounds at Palomar Observatory and the peak of the CCD response function. Futhermore, $g - r$ is suitable for providing quick and reliable classifications of young transients. As a stretch goal, the $i$ band is included, which is primarily driven by the EM counterparts to GW sources science goal. Current theory \textbf{(XXX best ref? XXX)} suggests that these EM counterparts will be very red, and the ability to search for such counterparts in the $i$-band will dramatically improve the yield for such discoveries.     \textbf{The Number of Filters Used in a Night}    The number of filters that can be used in the same night is constrained by the camera design. Target of Opportunity (ToO) observations require that either of the two primary filters, $gr$ (or three if the stretch goal, see above, is obtained), be available roughly within the time it takes the telescope to slew and acquire a new field.     \textit{Specification}: the number of filters available at any given time is specified as Nfilters Table~\ref{tbl:Nfilters}.  \begin{table}   \begin{tabular}{ rrrr }  Quantity & Design Spec & Minimum Spec & Stretch Goal \\   Nfilters & 2 & 2 & 3 \\   \end{tabular}   \caption{\label{tbl:Nfilters} The number of filters that can be housed in the camera.}  \end{table}  \textit{Specification}: the maximum amount of time necessary to exchange filters that are already present in the camera is specified as TFmax (Table~\ref{tbl:TFmax}).  \begin{table}   \begin{tabular}{ rrrr }  Quantity & Design Spec & Minimum Spec & Stretch Goal \\   TFmax (min) & 3 & 10 & 1 \\   \end{tabular}   \caption{\label{tbl:TFmax} The maximum allowable time, in minutes, allowed to switch filters that are already present inside the camera.}  \end{table}  This requirement is driven by the search for fast, young, and rare transients, as well as the search for EM counterparts to GW sources. Rapid filter changes will enable color measurements for fast varying transients, as well as filter dependent searches for EM counterparts to GW sources.