Hi Daniele,
Currently, we can't set the map zoom of the map view in the listing. Because the zoom value is hard code.
If user search city, zoom level is 16, if user only search state, zoom level is 10, if user only search country, zoom level is 7 and in default is 4.
You can edit those value in file
components > com_osproperty > templates > default > result.map.html.tpl.php
Thanks
Dam