Donating to disasters used to mean writing a check to Oxfam or the Red Cross.

These days in the Internet age, for the Ebola crisis, citizens from all over the world are donating their time by going online to build maps for relief workers.

Call it crowd-sourced cartography that can save lives.

Roads or paths to remote villages through deep forest in West Africa, bridges and river crossings, school buildings that can be used as temporary clinics, an open field for a helicopter landing - all these are visible from satellite imagery and provide critical information for delivering aid.

However, these details never made it onto official maps in Liberia, Guinea and Sierra Leone - countries too poor to worry about whether there are accurate Google Maps loaded onto smartphones.

So when the Ebola epidemic erupted earlier this year, Doctors without Borders, the American Red Cross and other groups on the ground found that unreliable maps made fighting the spread of the deadly virus much more difficult.

They could not trace the likely vectors of transmission because they did not know the patterns of peoples’ daily lives, and they could not plan effective aid delivery.

Enter the collaborative Ebola project by the Humanitarian OpenStreetMap Team (HOT).

OpenStreetMap is a project to create a free, open map of the world, built by volunteers through GPS surveying, aerial imagery, and public sources of geographic data.

Taking that concept a step further, HOT connects the OpenStreetMap community with humanitarian players on the ground to fill in the gaps on maps for disaster and crisis zones.

Around 1,200 volunteers so far have logged onto HOT's website, clicked on a map quadrant and traced in the rich geographic details visible from satellites.

A quick tutorial guides volunteers through the work, which is similar to using a software program like Adobe Photoshop.

By using the satellite imagery to add details like population density and connecting paths between communities, remote map makers give humanitarian groups vital tools for planning their ground campaign in combating a disease that has claimed more than 2,400 lives.

“They will print out the maps poster sized and pin them on the wall to plan their work, how to distribute supplies,” said Pierre Beland, a 67-year-old retired economist living near Montreal who has turned his computer knowledge to map making.

For Andrew Buck, an unemployed 29-year-old computer scientist who logs on daily from his home in Fargo, North Dakota, the map work transports him a continent away.

“You are acutely aware and start to get a sense of being in that place and learn about how people live, their farms, the fields, where the kids play soccer, the schools, and connections to the next village,” Buck said in a telephone interview.

VOLUNTEERS MAP DISASTER ZONES

Their work began in March after Doctors without Borders, the non-profit medical corps based in Switzerland, sent a geographer to Guinea to work alongside epidemiologists, who needed accurate maps of buildings that could serve as clinics and specialized maps showing pathways along which the virus could spread.

Audrey Lessard-Fontaine, the group's cartographic liaison, asked OpenStreetMap to enlist volunteers.

Its worldwide Internet community had experience mapping disasters. Their first assignment was in January 2010 mapping Port-au-Prince after the Haiti earthquake destroyed the government offices that housed its maps.

Nearly four years later, 1,500 OpenStreetMap volunteers from 82 countries mapped flooded homes and what was left standing after Typhoon Haiyan ravaged the Philippines.

The Ebola crisis is by far its largest project to date.

"The great thing about it is the speed at which areas can be mapped. Even if we had five staff full-time working on it, we would hardly be able to reach the speed at which dozens,hundreds of volunteers manage to map out a zone," said Lessard-Fontaine.

The volunteer cartographers have recorded 7 million data points so far and still have large swathes undone. By comparison, Typhoon Haiyan was 4.5 million data entries, and Haiti only 1.3 million, Buck and Beland said.

Their latest assignment came this week. Doctors Without Borders needs a detailed street map of Monrovia, the capital of Liberia, where the outbreak is raging out of control and U.S. President Barack Obama is sending 3,000 soldiers.

For the cartographers, it’s a way to fight Ebola from their desktops for which anyone can sign up.

“We’re just a bunch of computer guys on the Internet,” said Buck.