Why can't I use larga instead of longa?
Yes! Nobody says "a saia é ampla" (that's used for places - a sala é ampla). A saia é larga is much better.
Maybe ampla is used in fashion or tailoring?
I.e. a type of dress or skirt?
Hi Paul, here in Brazil we use longa as long (in English). Larga when it does not fit, drop on the floor.
Especially why not, since the correct translation for "The can is wide" is A lata é larga^?