relative image size and hotspots

Is there a graphic file format that supports:

transparency                  (alpha channel, or gif-like)              gif png svg
relative image size          (eg in CSS: img {width:10%;})        gif jpg png   but not svg
some form of hotspot      (imagemaps, alpha or...)                none known that support relative image size, imagemaps otherwise

SVG would appear not to support relative image size, as imagemaps aren't suited to this type of transform, ie they assume a fixed image size.

jonathan chetwynd