Surprised there isn't more construction along 9th Line yet, it's a very strange space.
Essentially the 9th Line lands are those that are between said roadway and the 407 tollway, and currently undeveloped:
https://goo.gl/maps/Z2J1eA9S7YW1NMEm8
Originally the lands belonged to Halton Region / Town of Milton as 9th Line was the dividing line between Halton and Peel Regions. When the 407 was constructed this left an odd vestigal space between the 407 and edge of Mississauga's urban area that didn't make a whole lot of sense. At the same time Halton Region didn't have much interest in developing them as they were focusing on their own growth areas, largely centred around Milton and the Uptown Oakville development area. So a lonnngggg and drawn out process to transfer the lands was undertaken with handover in 2010.
Development is tricky as generally speaking lands fronting 400 series highways are reserved for employment uses (industrial/office parks), and the area also has to accommodate space for the future 407 transitway. So there's not actually a whole lot of developable land and the City/Region wants to make the most of what's there, which means no tract subdivisions. Interactive concept map can be found here:
https://mississauga.maps.arcgis.com/...5bde061bff7636