[Xplanet-development] Making maps

[Svend H. <sh...@cy...>]

I am interested in learning how to make maps for xplanet.

The problem is that I have 4 million markers I want to show on the map.

So my idea is to color a pixel on the map for each marker point.

But since I have so many points, why not make a maker-map and then merge
it 
with a earth map to get a final map. Using something like 
xplanet -image day.jpg -cloud_image maker.jpg -shade 100 -output
day-maker.jpg -geometry widthxheight

But how do I build the maker-map ?
As I see it. I have to have a formula that can map a 
(latitude,longitude) to a (x,y) pixel coordinate.  

Do there exist any software that can make it easy for me ?

What information or code should I read ?

The map at http://www.geourl.org/ is similar to what I want to make.