Hunter College Cartographers
Workers at Ground Zero
Jeffrey Bliss, Research Associate at the CARSI Center, Hunter
College, reports on his experience performing vital mapping
work at Ground Zero.
We see a red light at the intersection of Second
Avenue and 57th Street, but since there is no cross traffic we
decide to run it. We pursue our scoff-law tendencies down
Second Avenue until we are finally halted and asked for
credentials at a checkpoint. I display my CUNY ID, and my
passenger, Al Leidner, a high-ranking City official, flashes
his. Our cargo raises questions, so we inform the sentry of
our mission and explain the purpose of three
computer-generated maps we have that are just minutes old.
Passage is permitted.
Several more checkpoints greet us as we
head toward the World Trade Center site through a city-scape
eerie in its absence of pedestrians, cabs, and almost all
vehicular traffic. Fire trucks and police cruisers ply the
streets like hornets circling a damaged hive. As searchlights
rove the sky in search of unknown objects, we finally arrive
at "The Bunker." We gain entry to the structure after rigorous
inspection of our personal possessions by more armed
With the events of September 11, I knew that my
life was to change, but could not comprehend the extent. It
was not until the next day that I learned the research
laboratory I worked in at Hunter College possessed the only
useable database of our city's geography and infrastructure.
The City's databases maintained in its emergency preparedness
office had been destroyed. It would be next to impossible to
conduct any type of rescue effort without the information this
digital data contained. When City officials saw the maps we
delivered, they instantly recognized that such maps would be
crucial to the rescue and demolition
Our lab, the Center for the Analysis
and Research of Spatial Information, known as CARSI, is
the brainchild of Hunter College professor of geography Dr.
Sean Ahearn. He formed it in 1994 to study the differences and
causes observed in measurable phenomena that exist in
three-dimensional, geographically oriented space.
being hastily enlisted in the smoky and dusty chaos of Ground
Zero, Ahearn brought together his CARSI staff of graduate
students, including myself, for several weeks of urgent work,
analyzing data and producing cartographic representations of
the landscape of disaster, some of them rolling out of a huge
54-inch-wide Hewlett Packard printer. While Ahearn never
envisioned his lab would be used in this grim fashion, he and
the CARSI staff are gratified to have been able to contribute
to the return of Lower Manhattan to the citizens of the city.
We have been particularly gratified to assist those who have
heroically and unselfishly endured work in the fragile,
risk-laden wreckage at Ground Zero. What follows is a brief
description of the cartographic stages of our work within the
CARSI lab and some of the images that were used at the site of
the World Trade Center disaster.
Our first cartographic product was a
hard-copy detail focusing on the WTC prior to the attack
(illus. B). This detail was taken from a spectacularly large
digital aerial ortho- photograph of all five boroughs that was
captured in 1996. (An orthophoto has had the distorting
effects of the earth's curvature removed.) This orthophoto was
assembled from 1,800 individual photos, gained through
fly-overs, into a single, seamless whole 130 feet tall by 125
feet wide. Needless to say, the entire image exists only in
digital form, at least until we commission the flamboyant
conceptual artist Christo to use it on one of his famous
This single large image had been produced as
the result of a mathematical process in which individual
sectors were brought together. A Global Positioning System
receiver was employed as each image was captured, producing a
quite impressive level of precision.
from 14th Street to Battery Park in our monster photo would
require a sheet of paper 16 feet by 14 feet, we decide to
reduce to half scale. Prior to printout, we labeled features
for easy reference—including overlays of infrastructure,
building footprints, and subway entrances; these large maps
were used by the Office of Emergency Management (OEM) for
planning. Smaller area-specific "scrolls" were printed and
distributed to rescue/demolition workers. It was soon deemed
necessary to create post-collapse geo-referenced photos, and
over- flights commenced on September 13th. We processed and
enhanced these preliminary images, printed them out, and
delivered them to OEM.
Smoke rising from the debris foiled the
first over-flown images, and so a new technology was
suggested: LIDAR or Light Detection and Ranging. In addition
to "seeing through smoke," this would also provide an
assessment of the cubic size of the debris field, since the
output of a LIDAR sensor is the elevation of objects. This is
because its laser beam operates at a wavelength not attenuated
by smoke. LIDAR first sends a light beam to earth from an
aircraft, then calculates the time it takes for the reflected
beam to return to the aircraft. Distance is then computed and
converted to height above sea level every 5 feet in all
directions of the selected area.
Advances in Geographic
Information Science (GIS) software and high-speed computers
give geographers tools to manipulate LIDAR's drab data (just
gray dots on a black background) and transform it into
striking color presentations. Seen here (illus. D) is a color
image created by converting the point data into a solid
surface and assigning color to elevation ranges. Areas of
orange are below street level, street level elevations uses
brown hues, and greens to blues represent height above street
level. This data set gave the first clear rendering of the
extent of damage. This data set was then converted into a 3D
image that could be viewed from all angles.
(illus. C) is such a 3D image looking south. WTC Building #7
is the seen as the round heap at low center. Just below it
between two streets, is BMCC's damaged Fiterman Hall. Areas of
orange are below street level. This data set was further
manipulated by conversion to a 3D image that could be viewed
from all angles.
Digital data is so much more protean
than its hard-copy counterpart! Once LIDAR data was converted
into 3D, other novel possibilities became apparent. For
example, we sliced the data model in half and then viewed it
from the side (illus. A), enabling us to view Ground Zero in
slices, much as Magnetic Resonance Imaging (MRI) allows
doctors to explore internal organs in
LIDAR data from July 2000 was also
compared with post-collapse data, allowing changes in
elevation to be discerned. Two post-attack LIDAR data sets can
be used similarly to quantify debris removal, settling, and
subsidence of the ground where damage to underground
structures might cause a further collapse.
concern over heat rising to the surface of the debris became
an issue, since areas of high heat could cause a softening of
materials and further collapse. CARSI was able to supply
images showing thermal flow (illus. E, with old WTC footprints
underlaid) through overflights with a thermal sensor. This
data was enhanced to show the hotspots and ignore all else.
New data was obtained daily, and a progression of this heat
was then mapped out.
CARSI continues to provide support
to Ground Zero in all manner of spatial analysis. The
destruction of New York's tallest buildings gave rise to
unconventional and extemporaneous techniques in data
interpretation. Though the challenge was daunting in its scale
and sense of urgency, we came away with some successes. Some
of our experiments didn't work, but that is where it is good
to be a graduate student. Given Dr. Ahearn's insight, we plan
to re-examine our efforts and solve some of the geographical
riddles exposed by the shattering events of
CARSI researchers will also be returning to
work on a variety of globe-spanning fronts. Asia, for example,
is the venue for tiger preservation research in Nepal and in
Thailand, and the New York metropolitan area is the site of
CARSI study of West Nile Virus dispersion. There are currently
two mapping projects, one in Puerto Rico, the other in Nepal.
Our largest work, however, is the NYCMAP project for the City
of New York. This cutting-edge enterprise will change the way
New York—and all cities—manage infrastructure, since all city
agencies will employ the same database and map to conduct
daily operations. The database will be maintained and updated
in such a a fashion that changes made by one agency will be
seen by all other agencies.
And it was the NYCMAP
project, after all, that provided us with the database to
support to the World Trade Center relief effort. With the OEM
back on its feet, more and more of our attention is now being
devoted to a tragic new CARSI speciality: the spatial analysis
of disaster. There is much more to learn.
courtesy of the CARSI laboratory.