So, the aspect ratio is right. Your problem is that you want it to be a perfect multiple of 7:4.
(...)
Detailed explanation at example: If there is a SVG-file on wikimedia, some fixed logic generates png-images for the flag's description page generally. The first image, here 800 × 457, is displayed very prominently always at the beginning of the SVG-description file, others (320 × 183 pixels | 640 × 366 pixels | 1,024 × 585 pixels.) follows as links.
All these sizes seems to be bounding-boxes from historic used (maybe even today) resolutions of (CRT-)monitors respecting aspect about ratio as near as they can If horicontal OR vertical is maximized to this resolution.
Those links as provided as convenience for downloading smaller versions. They were added per bug 2581. I think those were added as arbitrary sizes (with a large history usage, as noted).
Then some facts to the original SVG code is stated and than further fixed png-sized images follows as links (This image rendered as PNG in other sizes: 200px, 500px, 1000px, 2000px.).
The last , in small font set explanation, I added for people to get an understanding of the reasons lying behind the scene. :-/ [Only for thios flag].
This flag should have a ratio of 7:4 which has the SVG original, but NOT the prominantly displayed first image (800 × 457 , 800 is not divisible by 7, nor 457 by 4)!
So nobody should be allowed to get a thumbnail with eg. exactly 120px width? (As used in the galleries, meaning you would end up with differently-sized thubmnails, which would look bad)
Because in this flag, there are these two strips of "Alkmar Allah" Tekbirs, rendering artifacts can get easily visible if improper rendering occurs! First reason is: flag height in pixles is not divisible by 3, so the three green, white and red strip can't be of equal height (as demanded in the original SVG-code)! And because the Tekbirs should be exact aligned at the border of the green/white and red/white strip rounding errors may provocate a green or a red one-pixel-thick line to appear between the white strip and the Tekbir as you see in the 800x457 image!
So your problem is not the scaling itself but that it gets wrong (I don't see a red line above the letters or a green one below them, btw so seems to render fine).
It seems the scaling and rendering is doing in the wrong order (my guess, I also tried different work-arounds but got no satis- factoring solution, because it is not a coding issue in SVG!).
We are just asking rsvg to "render this svg in this size", not doing two different passes.
I guess: IF one would FIRSTLY render the original SVG to its orignal size into a fixed bitmap format and then scale this down to the wanted (png-)size, several visibale artifacts (like the just mentioned MUST be gone!). So, this is a rendering-design issue.
Well, if the given instance renders badly you should take the issue upstream to rsvg authors (unless the problem is that wikimedia is using an outdated version).
Moreover to avoid further artifically introducted problems by chosen thoughtless fixed sizes (500px), I propose NOT to use multiples of 100 or 1000 nor historican monitor sizes as fixed image sizes (which are out of control for the user/uploader!!), but sizes which consists on many small primes, i.e. HCN (highly composite numbers). Thus my second pointer in my first email to explain the background.
I'm pretty sure this will turn out to be a bad idea, but please propose the alternative sizes.
BTW: The same effect/statement is correct for SVG-templates like the one which uses national flags displaying in info-boxes in articles. But here maybe I can trigger guys responsible for these templates on XY-wikipedia (language specific).
Those templates usually request a fixed size, so not related to MediaWiki defaults.
I hope I have explained it righlty and (nearly) relevant completely now.
Thanks for your attention, Achim
Thanks for your explanation.