Hey,
One of the preferred freelancers and a apple platform developer here.
First of all, I am really impressed by your project's concept, its unique, interesting and something that doesn't exist yet in appstore. It can be a bliss for active travelers and adventurous.
Since you have explained everything in pretty much point to point, I dont need to explain the things app will do and such, instead I will lay out the work flow I have thought of which can be used.
So first of all, the main part of the app's functioning will be location services and background usage, since the user should get the drops even when the app is not open. For that, we will monitor user's location via the device's gps using low energy module and match it from our database of existing drops. Now a match, a Notification/Alert will be shown.
Now as per drops, we will again use the GPS hardware to save the latitude and longitude of the location user saves as a drop, they will be first saved in a backend database and then copied to local device (database copy) so that it can be used in a match in background mode.
When adding a drop, there is attachment icon, I suggest we instead use a camera action to let user take a pic and attach the pic instead (with his drop).
I do want to ask though, do you have a "logic" of determining which drops to show/match with determined or do you want me to come up with one ?
I have run out of character limit, feel free to reply to discuss in detail.
Regards