How do I download data for just a small area?

Yes, the maps are organized in sections across the country.

Go to Settings > Data Downloads and you will be presented with a map.  Find the state/region you would like to download and tap within it’s borders on the map, then select Download. This will download the charts, maps and airport information documents that apply to this region.

For most pilots, making sure Low Alt is selected at the top of the page will ensure appropriate maps are downloaded for lower-level operations.  Jet/turboprop will also need to tap High Alt and download those regions as well to ensure that high level enroute maps are downloaded too.