Field layout for the CANUCS observations of Abell 370. The background greyscale is the BUFFALO ACS F814W image. NIRISS and NIRCam module B are centered on the cluster core. The NIRCam observations are made with a slightly larger dither pattern (INTRAMODULEX 6) and a small position offset so that NIRCam images the region outside the NIRISS imaging field where spectra are dispersed onto the detector. The NIRISS dispersion directions for the two gratings are shown with arrows. The NIRCam prime dither pattern is clearly visible (note that only the NIRCam Short Wave detectors, not Long Wave, are shown for clarity). When NIRISS is prime the dithers are smaller and barely perceptible on this plot. The full NIRCam Flanking Field is covered by BUFFALO optical imaging. The three NIRSpec MSA configurations in the field are not shown as their exact positions and orient angle will be defined later.