OpenStreetMap
On 24 June 2017, a big landslide occured in China’s Sichuan province, burying dozens of villagers alive. Although pictures from the ground clearly showed that most victims didn’t have a chance for survival, satellite imagery shows the scale in one glance:
(source: ESA Copernicus Sentinel 2. 19 February 2017 and 7 September 2017.)
Some OSM users started mapping buildings in the area immediately afterwards. Pretty much the entire built-up area of one village was buried.
Thanks to the freely available Sentinel-2 data, you can map objects as recent as a month old. It’s a shame not much of the data is available in a readily usable image format, for now, processing it can be a time consuming job.
Discussion
Comment from imagico on 6 October 2017 at 14:13
Good example for the usefulness of open data imagery for mapping in OSM.
The limiting factor in this area by the way is not the recording frequency - both Sentinel-2 and Landsat have newer images available than from September 7. But cloud cover during summer leads to most of the images not being useful.
And care should be taken to process the data into images well readable by the mappers so they can correctly interpret what they see. Here a rendering of the same image that probably better resembles the on-the-ground impression: