On Sat, Feb 4, 2017 at 3:38 PM, Luca Libonati <luca.libonati@gmail.com> wrote:
Hi Gergo,
is this the right way?

It could be, although there is not much point in using a generator in itself (generators are meant to provide input for other API modules, e.g. you could add prop=imageinfo to the URL and get thumbnail URLs and whatnot for each image). If you just want to use it on its own, you can call it as action=query&format=xml&list=search&srprop=size&srsearch=london&srnamespace=6&srlimit=10&srgiprofile=wsum_inclinks&srenablerewrites=1
If so, could you help me to understand how can I set a defined size?
Moreover, I see that there is also paragraph that talk about search for specific file measures. Is this active? How could I use it?

For a minimum size, you'd be  using something like gsrsearch=london%20filewidth%3A%3E800 (ie. "london filewidth:>800", URLencoded).