180,000

The NYPL has posted 180,000 public domain images to "use and share;" which is cool enough, but you've got to see & browse them all at once on this huge mosaic to appreciate the scope of the enterprise!

They also have also done a mash-up of "Green Book" data. In the age of segregation, the Green Book listed hotels, restaurants, bars, and gas stations where black travelers were welcomed. Map out trips you would take with this tool. Plot a trip between two US cities and see where you would be "allowed" to dine and rest.