Fischer projection
= Fischer projection
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In a <Fischer projection>, each cross represents a <carbon> position: horizontal <chemical bonds> point toward the viewer and vertical <chemical bonds> point away. For the open-chain <aldehyde> <sugars> illustrated here, place $\mathrm{CHO}$ at the top and $\mathrm{CH}_2\mathrm{OH}$ at the bottom. This is a convention for <stereochemistry>, not a measured molecular shape. See https://iupac.qmul.ac.uk/stereo/FM.html#Fischer[Moss, IUPAC Recommendations 1996: Fischer projection].
In these <Fischer projections>, D specifies that the <hydroxy group> at the lowest <stereocenter> lies on the right: C4 for <ribose> and <deoxyribose>, C5 for <glucose>. D does not specify every other <stereocenter>, and it does not specify the direction of rotation of polarized <light>. See https://openstax.org/books/organic-chemistry/pages/25-3-d-l-sugars[McMurry: the meaning of D and L].