Where to start for a tile grid for an android game?

I am trying to create a tile/grid world map for an Android game. The world map (1000x1000) is one huge ocean with islands that will be the individual players. I have been looking for a tutorial on the Unity website and many Google searches with no luck. After the map is created, the individual coordinates(00,00 - 999,999) will be clickable. An example of this type is Kingdoms of Middle Earth or War of Warship Pacific War. The world map will be in a 2D array and the view able area will be 9x5 on the phone and will update the area when scrolling around the map. For the world, the sprites will be one of two things, a player island or ocean. Think of a graph paper, the top left box is 00,00, and the bottom right box is 999, 999 I am new to Unity and can code a little, but I am familiar with arrays. Any help in a direction or a useful tutorial would be appreciated.

Thank you in advance