The map, created by Brooklyn web developer Jill Hubley, is based on data collected in 2005—an updated tree census to be taken this year will include the many additions from the MillionTreesNYC initiative. Still, each of the city's 592,130 trees extant during that time are represented, viewable as one large, colorful lump or by individual species. You can opt to use a base map if you're still not quite sure which blob is Queens, or go rogue and turn it off.
The map is enthralling to explore even if you're not a big fat data geek—notice the dense concentration of red in Lower Manhattan? Those are London plane trees, identified as the most common species in the city, likely because of their exceptional resistance to diseases and tolerance for urban environments. Does something smell like semen? That's because Manhattan is blanketed by Callery Pear trees, or because you...are standing near some semen. This is what science feels like!
Hubley herself was surprised by what the map revealed. As she told the Atlantic's City Lab:
I would've thought the trees throughout the city would be fairly homogeneous in terms of the percentages planted. Instead, Brooklyn has more London Plane trees than any other species (23.6%), Queens has a ton of Norway maples (18.3%), the majority of Manhattan's trees are Honey locusts (23.3%), and Staten Island has a high percentage of Callery pears (24.8%). The Bronx has the most evenly distributed assortment of trees—Honey locust, Norway maple, and London Plane tree are all popular (11-13% each).
Hubley also notes that "tree selection varies per site based on site condition, overhead clearance and tree bed width," which the Parks Department uses to define the habitat for each planting area, and from that, determines the range of species that can be planted there.
Enjoy, and get thee to the nearest tulip tree!