Have you just begun playing survivor z?
If you have it will take a bit of time before you can claim a location and turn it into a stronghold
When you are able to do this, you will go to a park for example
You clear it of zombies then it will ask if you want to claim the land
If you do click scavenge and claim the land as a stronghold
It just takes a bit of time
You may need to return to same place several times before you can claim it