One way that you may be able to find maps that someone has already created is to use ArcGIS Living Atlas of the World (Living Atlas). Living Atlas is "a curated collection of authoritative, best of breed content from Esri, Esri partners, and the GIS user community".
1. Click on "Continue your story..."
2. Click on "Map".
3. Click on "Living Atlas".
4. Use the search box to search for a topic. In this example, I typed "Milwaukee".
5. If there is one, click on the tile for the map that you are interested in.
6. Focus the map and place it in your StoryMap.
6a. You can turn on layers of interest. Note that you might have to zoom in or out to make some of the layers visible.
6b. If bookmarks are available, you can click on one of those to highlight a specific area.
6c. Choose your Options. In this example, I chose "Legend", "Keep legend open", and "Overview map".
6d. You might have to move the map around to get the focus just the way you want it. I moved the map to the right so that the legend doesn't obscure the map too much.
6e. Click on "Place map".
7. You can add elements to the right or left of the map, and change the size of the map from the pop-up edit bar.
8. Publish your changes.
