It took just 48 hours after the earthquake hit Nepal for a global network of volunteer geeks to fill in big gaps in the nation's map for relief workers on the ground.

In a country known for its poor roads, which are still passable? Which patches of land can serve as helipads, or, lacking space, drop zones? Where are the landslides? And how many structurally sound buildings will aid workers fine once they arrive?

Answering those questions is the goal of crisis mapping, which has become an important assist to first responders in Nepal as they try to untangle logistics and respond to needs for medical care, shelter, and food and water since calamity struck last Saturday.

The  “digital humanitarians”