SVGs can respond to their size, yes -- essentially the same way websites can -- see https://codepen.io/pjwdev/pen/dypVLgg

In addition, vector-effect="non-scaling-stroke" allows you do declare that a line is [eg] 1px thick, regardless of the image size.

Snapping to sizes would be possible, but not straightforward, until CSS supports calc(round()) https://www.w3.org/TR/css-values-4/#round-func