Using the latitude and longitude gets the tile image with the location in it, But how to pinpoint that location?

I am given a latitude and longitude of a place. Then I ap开发者_如何学编程ply global mercator projection formula. Then I am able to get a square image(256*256) with the location in it. I am using all this to display a map made my images from a customised google map, in my iphone app.

When zoom is high, even when we pinpoint randomly on that image, it will be ok. But when zoom decreases, that single image may constitue an entire nation sometimes and my pinpoint will be in another nation(on the same image).

Is there any mathematical or someother formula or something else which will help me to pinpoint the exact location of that place in that image?

I am not an expert on map projections, but you might check to see what projection Google uses. When you change the zoom level, your pin may be misplaced because the motion of your chosen location, using Mercator, doesn't come out the same as for Google.

Hope this helps.

John Doner