Easily level up Emergency Shelters
To quickly and easily level up an Emergency Shelter, leave the shelter, find a survivor event (shown by a blue “?” icon), and a survivor will call for help. Kill all the nearby zombies and the survivor will return to your shelter. Run back to the shelter, then repeat the process as many times as desired. Survivor events will keep respawning after you return back to the shelter. The following are two survivor event locations next to shelters early in the game:
Willamette Memorial Megaplex: There is a survivor event at the top of the stairs to the underground parking entrance between the Central Plaza and Amazon Food Court.
Old Town: There is a survivor event in the parking lot behind the church and near the cemetery entrance. It is very close to the Old Town Emergency Shelter.
You only need to reach Level 3 by saving four survivors to unlock the most important vendor upgrades —- including key item locations on your map.