I would venture to say that the landfill should be spawned but in a region outside a city.
Logging camps, iron mines, coal mines and bauxite mines do well when spawned, but I also place at least one so that if you aren't quick getting to a region they don't begin disappearing. This also allows for them to come about based on service to an area.
Other than that, I would say that most general industries can be spawned, but it depends on the map maker. Bear in mind that you always want to make sure that the player can make what they need.
Limited industries, like Legislatures, Military bases, etc, shoud be placed.
At least that my opinion, and others may have differences after playing and creating maps.