Lightning density map

Hi ,

I am trying to plot a cloud-to-ground lightning density map for Romania. The
data set contains: date(year/month/dat), time(hh/mm/ss), latitude, and
longitude for each lightning flash. The density maps were based on dividing
the study area into a grid cells (e.g., 20-km to correspond with the audible
range of thunder). I have used ArcGIS to calculate a density value for each
cell by counting the number of lightning flashes within the cell and
dividing by the cell area. The density value (flashes km-2) is then assigned
to each cell.

Can someone help me on how to do this in R?

Thank you very much,

Bogdan