I am always amazed how well RTH works in my flights. I fly in/over inaccessible terrain in the desert badlands at distances up to a mile away and for me the safest method for returning to "home" is by making certain my RTH altitude is set above all obstacles then letting the Spark handle all aspects of power management and navigation to return home until I have line of sight for landings.. Most times I let it land itself since it lands within inches of where it took off. I always ensure the Spark is moving along the vector/line on the map toward my "H" home point just to make sure all is working well and have never had any problems using non-dynamic home point (point of take off) and RTH.
On the map topic, the "Offline Maps" (
click thumbnail below) is not in the flight screen used when flying, it is in the first Intro Screen using the upper right menu.
The map is separate from the home points in that the home points are icon representations of lat/long coordinates that are plotted onto it from real-time data transmitted by the Spark to your device or through the controller. The map is static graphic information that is stored on your device as a basemap to display those points onto. The only time you would need the internet would be to obtain/download base mapping you do not have stored on your device for new location you travel to for flying. I have a feeling the app automatically downloads maps based on your location as you setup the drone since I have never had to manually download maps and I normally fly within about 15-mile radius away from my home. If you were to travel to new places some distance from your home then it would be a great idea to use the "Offline Map" function to create maps for that region.
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