How to get 1:1 scale in Keynote, Pages or Numbers?
If you select 'Actual Size' (Command 0) under the View &gt; Zoom menu, then the page should display at ... actual size.
With this setting, an A4 page on the screen is the same size as an A4 piece of paper that I hold in front of the screen. This works for Retina displays and non-Retina displays.
Back in the old days, Mac screens had 72 pixels to the inch. So it was easy for 1 point on the page to equal 1 pixel on the screen. This ratio is what become 100% zoom.
Of course, screen pixel density has increased massively since then. Pre-Retina displays were around 109 dpi. Retina screens are twice that, but scale everything up by 2, giving the same perceived resolution.
109 dpi divided by 72 dpi gives you 151%, which is the zoom factor you get when you select 'Actual Size'.

Preview has a Preference to define 100% as either 1 point = 1 pixel, or 'size on screen equals size on printout', which presumably sets 100% to the Actual Size.