Handle the display of multiple cities. At low zoom levels, the names of available cities should be displayed.
The map layer settings panel will have to be reworked to also support controlling different cities. In general, it should only show the options for the region(s) that is currently being viewed. This only applies if a high enough zoom level is being used. In some cases, multiple regions may need to be displayed, so the panel will need to be capable of handling multiple regions together.
Lastly, the data for each region should be loaded dynamically, and lazily. (#26)