I heard Étude de masses before but it’s more when they talk about a study concerning a community, like some kind of survey they do in society for election or subject like racisme. A journalisme term in other words.
About your term, in architecture, we are using “Étude volumique”
I found this on the reverso context website: (better than google translate to me)
Plan de masses? In France, this would represent the layout of the different “masses” or constructions on a given piece of land. Maybe it is volumes study in Canada… I don’t known…
Google translator shows “étude de masse” .But later I tried to translate this through the translation service Subtitling Services | Translate Video into 50+ Languages and the result was “Étude volumique” like the first comment. I am also more inclined to believe this answer than google translator. The context solves a lot, it is a pity that machine translators cannot do this
“étude d’implantation” is used more on a 2D drawing, to show the position of element on a terrain. Per example, when I draw a site plan for a festival, or a site layout on a cirque du soleil big top show. I use this term precisely for the plan we draw to see if the show fits on a prospect site.