Overlay a grid on a map

Hi,

I have produced a map (using the worldmap function) with latitude limits of 55 to 65 and longitude limits of -5 to 10. I want overlay a grid of 10 km squares which covers this area as well. Can anyone suggest a function similar to meshgrid which can be plotted on a map?

Additionally, later I want to assign values to each of these squares to create a heatmap like figure, so a function which allows me to assign a specific value to each square individually would be useful.

Thanks