How do I unlock new maps - PS4

On PS4, I completed The Bog on single player, unlocked all garages and vehicles, and then played and completed a couple of multi player maps, and also completed the first 4 challenges with 3 stars.

When I go back into single player, I can't choose any map other than The Bog.

How do I unlock new single player maps?

@carl-silvers you will unlock new maps by completing the maps objective, wich is delivering wood.
If you open the map, in the left sidebar it will show you what the exact objective is.

I also delivered all the log loads, so I don't know what I did wrong? Do loads to lumber mills have to come from specific areas?

@carl-silvers you can pick them up at the logstation (casual) or logkiosk (hardcore) note* that for hardcore mode you need a crane to load them. If you have delivered 8 points per sawmill it should be done.

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