New York City's urban forest provides numerous environmental and social benefits, and street trees compose roughly 25% of that canopy.1 While I had seen some numbers on the percentage breakdown of species throughout the city, I was interested in looking at the composition in detail. I wanted to see what patterns took shape in various neighborhoods, and across the city, and to see how the density of trees shifted.
To this end, one can explore the map in two ways: by using the tooltips and zoom function to identify particular trees, or by using the filter option to see the distribution of each species. I've also provided the option of disabling the base map for a starker, more abstract view.
The map represents trees surveyed during the last tree census, in 2005. The next tree census is happening this year. I'll update the map when the new data is released. Additionally, in January 2015, I filed a FOIL request for the 1995-1996 tree census data, though have yet to receive it. After some back and forth, I've been told I should get the results of the FOIL request at the end of April.
The map makes clear the most prevalent trees in each borough, while simultaneously revealing clusters of diverse species. Tree selection varies per site based on site condition, overhead clearance and tree bed width. The Parks Department uses these criteria2 to define the habitat for each planting area3, which in turn determines the range of species that can be planted.4
In addition to ensuring the selected species is a good fit for its environment, biological diversity is also an important consideration. Diseases and pests that target particular types of trees make varied plantings a necessity.5
How the map was built
The CSV files from the portal don't include geodata, so I downloaded the shapefiles, opened them in QGIS, reprojected them to web mercator, added geometry columns to the attribute tables, then exported each table to CSV.
I built the map using cartodb.js and leaflet.js, with a little SQL to do some filtering and joining. The data is hosted on CartoDB, and had to be split between a few different tables. Part of the reason for the split was that no one table could exceed 500,000 rows (there are roughly 600,000 trees on the map.) There is also a separate table with the common name of each tree and its corresponding tree code. The original data only included these tree codes, e.g. PLAC for London Plane. The first two digits of the code are the beginning of the tree's genus (in this example, Platanus) and the last two digits are the beginning of the particular epithet for the species (in this example case, acerfolia.) While the codes were probably helpful when cataloging the trees (and they do keep the size of each borough's census data smaller), they are meaningless as labels.
1 Trees Count! 2007 Report
2 Parks' Planting Process
3 A New Method for Streamlining Tree Selection in New York City by David Moore, Forester, New York City Parks Department
4 NYC DPR Tree Species Tolerance Guide
5 Visual Similarity and Biological Diversity: Street Tree Selection and Design Bassuk, Nina,. Trowbridge, Peter,. Grohs, Carol