One of the most common errors when editing the maps is when an editor creates a road and does not confirm the road by setting the city and road name (or stating it has none).
Duplicate cities can be caused by incorrectly named segments and should be corrected following the guidelines in the duplicate cities article.
Some states and territories manage a separate page on cities and towns to identify the specific city names that should be entered, and no others. For states that do not have a separate page to track the names, see this Wikipedia link and find the state or territory in question.