<i>Euclid</i> preparation

<jats:p><jats:italic>Euclid</jats:italic> is a mission of the European Space Agency that is designed to constrain the properties of dark energy and gravity via weak gravitational lensing and galaxy clustering. It will carry out a wide area imaging and spectroscopy survey (the <jats:italic>Euclid</jats:italic> Wide Survey: EWS) in visible and near-infrared bands, covering approximately 15 000 deg<jats:sup>2</jats:sup> of extragalactic sky in six years. The wide-field telescope and instruments are optimised for pristine point spread function and reduced stray light, producing very crisp images. This paper presents the building of the <jats:italic>Euclid</jats:italic> reference survey: the sequence of pointings of EWS, deep fields, and calibration fields, as well as spacecraft movements followed by <jats:italic>Euclid</jats:italic> as it operates in a step-and-stare mode from its orbit around the Lagrange point L2. Each EWS pointing has four dithered frames; we simulated the dither pattern at the pixel level to analyse the effective coverage. We used up-to-date models for the sky background to define the <jats:italic>Euclid</jats:italic> region-of-interest (RoI). The building of the reference survey is highly constrained from calibration cadences, spacecraft constraints, and background levels; synergies with ground-based coverage were also considered. Via purposely built software, we first generated a schedule for the calibrations and deep fields observations. On a second stage, the RoI was tiled and scheduled with EWS observations, using an algorithm optimised to prioritise the best sky areas, produce a compact coverage, and ensure thermal stability. The result is the optimised reference survey RSD_2021A, which fulfils all constraints and is a good proxy for the final solution. The current EWS covers ≈14 500 deg<jats:sup>2</jats:sup>. The limiting AB magnitudes (5<jats:italic>σ</jats:italic> point-like source) achieved in its footprint are estimated to be 26.2 (visible band <jats:italic>I</jats:italic><jats:sub>E</jats:sub>) and 24.5 (for near infrared bands <jats:italic>Y</jats:italic><jats:sub>E</jats:sub>, <jats:italic>J</jats:italic><jats:sub>E</jats:sub>, <jats:italic>H</jats:italic><jats:sub>E</jats:sub>); for spectroscopy, the H<jats:italic>α</jats:italic> line flux limit is 2 × 10<jats:sup>−16</jats:sup> erg<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> at 1600 nm; and for diffuse emission, the surface brightness limits are 29.8 (visible band) and 28.4 (near infrared bands) mag arcsec<jats:sup>−2</jats:sup>.</jats:p>