If the point of interest (POI) falls perfectly in the middle, the device needs four tiles in one dimension by three tiles in the other, for a total of 12. This would almost never happen and the device would need to download one more row and column of tiles along each dimension for a total of 20 tiles. Each tile is stored in the PNG format and would average around 20 KB each for land areas. That means that one iPad map display would be about 300 KB.
At 300 KB per map, it is possible to calculate the cost of each screen-sized map relative to the available data plans. For the $15/250 MB plan, one could download approximately 83 screen displays – about 18 cents for a screen-sized map. For the $25/2GB data plan, one would get 667 maps at about 3.7 cents a map. In comparison, a Rand McNally road atlas is less than $10 and the maps can be used multiple times.