We are hoping to add this highly requested feature in one of our next versions of PocketEarth.
In the current version of PocketEarth, if you are done with a place you just un-star it, and next time you do a data update, only your stared places will be downloaded again and other data will be deleted automatically. If you don’t want to wait for the next data update, you could use the Delete All option, and then re-star the places you want again. But this is not always ideal, so we will add a confirm dialog when you un-star a place, to ask if you want to delete its maps immediately.
The most convenient thing for users would probably be to make area downloads available by zoom level (download either a city, the state/province, the whole country, or a whole region in some cases). I’m not sure if the app is already doing this in some way, but it isn’t always obvious.
For example, when I tried to download map data for Guam, I would have wanted to download data for all of the Marianas islands at once, or maybe even all of the Micronesian and other Pacific islands as well, since they are so small. But the app restricts downloads to one island at a time, and the download for Guam was labeled for the Guam village of Dededo (lots of other villages exist on Guam, but nobody would ever just download map data for Dededo!).
Suggestion: make map data downloads available by a set number of larger regions — North America, South America, Europe, Asia, Africa, Australia/New Zealand, Oceania. Then also make it available by country or state/province. Then by individual cities as well, if need be.