The last day of TEDGlobal 2009 kicked off with landscape biologist Eric Sanderson, who gave a thrilling look at the Mannahatta Project– a re-envisioning of Manhattan in its original, 17th-century glory. This Google Earth of ancient New York definitely wowed the TEDsters on Twitter:

Eric Sanderson: Amazing how many water sources have disappeared from NYC since Revolutionary Days. He looks for lost features of NYC. — ruthannharnisch

Eric Sanderson doing a marvelous job of historical mapping. Great use of GIS, anthropology, history and ecology. A world that once was — pragzter

Sanderson should get funding to map the world before we destroy it! We owe it to our kids! Cmon TED give him support! — rom

Eric Sanderson opens Session 11, “Cities Past and Present,” with fascinating maps on optimal citibility — brainpicker

Amazing talk by Eric Sanderson: Manhattan as you’ve never seen it. Beautiful. — nauiokaspark

If you’ve got something to say about one of the speakers and you have a Twitter account, please make sure you’re using the #TED hashtag or replying to @TEDGlobal.