Theme maps

Hi,

I posted the same message on the forum but maybe I'll get better answers here.

I'm starting mapping with Drupal and I have a lot of questions and I'll be glad to get some help from someone who knows a bit in that field.

I'm very impressed with what Development Seed has done in monitoring Afghan elections: http://2010.afghanistanelectiondata.org/

They give some explanations here: http://developmentseed.org/blog/2010/oct/13/adding-interactivity-complex...
But that's a bit complicated for me...

I know how to put nodes on a map, what I'm wondering is how to theme the map so it shows some nice graphics. For example make the circle proportional to the number of nodes.

You can see an example here: http://www.sudanvotemonitor.com/ . This is not Drupal but Ushahidi, was wondering how this is done? (modules? CSS?).

Also is there people here interested in mapping human rights violations?

Thanks

PS: forum link: http://drupal.org/node/1056546