The data for this map was collected by the moderate resolution imaging spectroradiometer aboard NASA's Terra and Aqua satellites, and it shows the extent of fires across the globe in August 2014. Although many fires are natural (and an important part of the ecosystem), most fires around the world today are caused by humans. Scientists estimate that humans burn an average of 175 million acres of forest and grassland every year, often to make room for agriculture and living space.
In this image, the largest patch of active fires can be seen burning throughout sub-Saharan Africa, mostly because of seasonal savanna land management. You can fiddle with NASA's map widget to see how fire trends shift across the globe depending on the time of year.