MKMapKit Hexagon or Square Overlay

I want to make overlay with hexagon or squares over google map with MKMapKit. Not just one hexagon or square, i want to use google map like a tile based map with full overlay with hexagons in every 1km area.

I know app will crash if i do the overlay in one process so i want to do it only on the viewable portion of the screen but in that case i have difficulties to make the distance from the start point, its not getting on the right point or hexagons are not same size everywhere etc.

My question:

lets think i have 1 thousand hexagons in the viewable portion, so what is the best way to place them with a equal distance at once, how should my calculation ? if i scroll the map, how should i calculate the new start points.

or should i give up from hexagon and use another think ?

i hope i give you a clue for what i have try to do, any helps, any examples or any ideas are welcome.