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196 Machine Learning for Real-time Urban Metrics and Design Recommendations 1 User test on CityMatrix - an urban decision support system with a tangible user interface which provides real-time urban metrics and design recommendations Yan Zhang MIT Media Lab Arnaud Grignard MIT Media Lab Alexander Aubuchon Northeastern University (CCIS) Kevin Lyons MIT (EECS) Kent Larson MIT Media Lab 1 ABSTRACT Cities are growing, becoming more complex, and changing rapidly. Currently, community engagement for urban decision-making is often ineffective, uninformed, and only occurs in projects’ later stages. To facilitate a more collaborative and evidence-based urban deci- sion-making process for both experts and non-experts, real-time feedback and optimized suggestions are essential. However, most of the current tools for urban planning are neither capable of performing complex simulations in real-time nor of providing guidance for better urban performance. CityMatrix was introduced to address these challenges. Machine learning techniques were applied to achieve real-time prediction of multiple urban simulations, and thousands of city configurations were simulated. The simulation results were used to train a convolutional neural network (CNN) to predict the traffic and solar performance of unseen city configura- tions. The prediction with the CNN is thousands of times faster than the original simulations and maintains a high-quality representation of the results. This machine learning approach was applied as a versatile, quick, accurate, and computationally efficient method not only for real-time feedback, but also for optimized design recommendations. Users involved in the evaluation of this project had a better understanding of the embodied trade-offs of the city and achieved their goals in an efficient manner.

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196

Machine Learning for Real-time Urban Metrics and Design Recommendations

1 User test on CityMatrix - an urban decision support system with a tangible user interface which provides real-time urban metrics and design recommendations

Yan ZhangMIT Media Lab

Arnaud GrignardMIT Media Lab

Alexander AubuchonNortheastern University (CCIS)

Kevin LyonsMIT (EECS)

Kent LarsonMIT Media Lab

1

ABSTRACTCities are growing, becoming more complex, and changing rapidly. Currently, community

engagement for urban decision-making is often ineffective, uninformed, and only occurs in

projects’ later stages. To facilitate a more collaborative and evidence-based urban deci-

sion-making process for both experts and non-experts, real-time feedback and optimized

suggestions are essential. However, most of the current tools for urban planning are

neither capable of performing complex simulations in real-time nor of providing guidance

for better urban performance.

CityMatrix was introduced to address these challenges. Machine learning techniques were

applied to achieve real-time prediction of multiple urban simulations, and thousands of city

configurations were simulated. The simulation results were used to train a convolutional

neural network (CNN) to predict the traffic and solar performance of unseen city configura-

tions. The prediction with the CNN is thousands of times faster than the original simulations

and maintains a high-quality representation of the results. This machine learning approach

was applied as a versatile, quick, accurate, and computationally efficient method not only

for real-time feedback, but also for optimized design recommendations. Users involved in

the evaluation of this project had a better understanding of the embodied trade-offs of the

city and achieved their goals in an efficient manner.

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197

INTRODUCTIONRapid urbanization brings tremendous challenges. In China

alone, more than 250 million people will move to the city

over the next 12 to 15 years (Grimm 2008). Historically,

each major city had a unique identity, but newly developed

areas of cities today look stunningly similar. Many are

being developed too quickly and without regard for the

future inhabitants. In the urban decision-making process in

developing countries, there is typically a lack of community

participation (Midgley and Hall 1986). We believe that partic-

ipation could be more effective with rapid-prototyping tools

that enable both experts and non-experts to explore multiple

scenarios collaboratively. Designing and planning with

traditional tools (sketching on a zoning map or Computer

Aided Design (CAD) software) requires years of training,

making them difficult to use in a public collaborative envi-

ronment. While emerging urban simulation tools are capable

of analyzing the input of a proposal on multiple aspects of

urban performance, most tools are difficult to learn and

time-consuming in terms of computational resources. This

makes the process expensive, inefficient, and non-intuitive.

To address the urban challenges above, CityMatrix (Zhang

2017) was developed as an urban decision support system

with an intuitive, tangible user interface, real-time feed-

back of multiple urban simulations, and optimized design

recommendations. It was designed with the goal of facil-

itating public engagement with both professionals and

nonprofessionals. With CityMatrix, stakeholders can rapidly

and collaboratively explore many possible configurations

of a proposed urban environment without prior knowledge

(Figure 1). Technically, CityMatrix uses machine learning

algorithms to predict multiple urban simulations and

provides a versatile, fast, accurate, and low-cost method

compared to traditional options.

RELATED WORKCityMatrix was developed with a multidisciplinary approach

that focuses on three main fields: tangible user interfaces

(TUI), urban simulations, and machine learning (ML). Recent

advancements provide a solid foundation for our work.

Tangible User Interface

Prior work of the Tangible Media group and City Science

group (formerly Changing Places group) at the MIT Media

Lab explored using TUI to improve the accessibility and

efficiency of urban planning. The "Urp" project (Underkoffler

and Ishii 1999) from the Tangible Media group provided

users with digital shadow and wind simulations in an urban

environment. When the users manipulated the physical

buildings with optical tags, the shadow and wind simula-

tions updated accordingly.

Urban Simulations

Professional urban designers normally run urban simu-

lations, such as traffic, solar, wind, thermal, etc, after they

have a design proposal. For nonprofessionals, intuitive,

real-time feedback is critical for understanding the impact

of urban decisions and achieving their goals. However,

many more complex simulations can take several minutes,

even hours to run. Traditional approaches to speed up the

simulations include decreasing the simulation resolution,

parallelization of computation, and multilevel modeling,

none of which provide real-time feedback with enough

resolution without consuming excessive amounts of

computational resources. To achieve a complex simulation

in real-time, an unconventional approach is required.

Machine Learning

Over the past few decades, novel techniques in the fields of

machine learning (ML) and artificial intelligence (AI) have

led to new breakthroughs in the ability to evaluate trends in

vast datasets in order to make powerful predictions. Simple

regression and support vector machines achieve state-of-

the-art results in basic classification problems, while other

datasets require more powerful models to derive semantic

understanding. Large-scale image classification with the

ImageNET dataset was made possible through the use of

deep convolutional neural nets (Krizhevsky, Sutskever, and

Hinton 2012). Reinforcement learning algorithms allowed

for state-of-the-art performance against human subjects

in the game of Go with the AlphaGo framework (Silver et

al 2016). Time-series prediction with recurrent neural

networks achieved expert-level results in detecting heart

arrhythmias with the use of ECG lead signal data with

ground truth annotations (Rajpurkar et al 2017). With many

of these techniques still rapidly evolving and growing, the

potential for applications of machine learning is nearly

endless. Here, we seek a novel machine learning applica-

tion to use for urban planning and decision optimization as

a way to support current human-driven approaches.

METHODOLOGYDesign of CityMatrix

The setup of CityMatrix allows the users to change the

layout of land use by moving optically-tagged modules. Each

cell can be changed into six types of buildings, roads, and

courtyards. The users can add, remove or exchange the

existing bricks, or pick from an external library of pre-as-

sembled Lego brick modules (Figures 2 and 3).

The slider and selection dock on the side allows users

to change urban density. Users could put one of the six

building types into the selection dock (lower right) to select

all the same types of buildings in the city district. They could

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2 4

then slide the building height slider up or down to manipu-

late the height of these buildings, changing urban density

(Figure 4).

The visualization output of CityMatrix includes the urban

configuration and the urban performance heat-maps on

the TUI table, and the 3D representation of the city and the

urban metrics radar-chart on the vertical display (Figure 2).

Hardware Structure

CityMatrix is composed of the following components (Figure

5):

• A modular prefabricated table;

• Pre-defined Lego bricks, for which the top is flat, and the

bottom is an optical tag composed of four colored Lego

pieces (Figure 6);

• A diffused surface LED to light the optical tags;

• A webcam to capture video feed for a computer vision

algorithm to decode the optical tags at the bottom of all

Lego bricks (Figure 6);

• A portable computer that runs the software;

• A high definition, high brightness projector, which proj-

ects two-dimensional representations of the city onto

the Lego bricks;

• A vertical screen for displaying a radar-chart and the

three-dimensional representation of the city.

Software Structure

The CityMatrix system architecture contains 4 main layers

(Figure 7):

• User Input: The system collects the user input by

reading the optically-tagged Lego bricks and decoding

them into building types and heights.

• Urban Performance Evaluation: The system runs calcu-

lations to evaluate the five aspects of city performance.

The evaluations are on both local scale (heat-map) and

aggregated scale (radar chart scores).

• Optimization suggestion: The system takes the machine

learning prediction as an evaluator and then searches

and evaluates a large number of possible options for the

next move, providing users with an optimal option.

• Visualization Output: The real-time feedback and optimi-

zation suggestions are visualized on both a TUI table via

projection mapping and a screen display. These visual

outputs will give the users key information to support

their decision for the next step.

Urban Metrics

With CityMatrix, users can examine five urban metrics:

population density, experience diversity, energy efficiency,

traffic performance, and solar radiation. The first three

metrics can be caculated in real-time but traffic and solar

simulations are time-consuming.

CityMatrix incorporates an Agent Based Modeling (ABM)

module developed on the GAMA Platform (Grignard et al

2013), a modeling and simulation-development environment

for building spatially explicit agent-based simulations. In

such an approach, urban phenomena are modeled by a

composition of autonomous entities, called agents, oper-

ating in an environment where they interact and organize

3

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5

Projectorfor TUI table top

Vertical Displayfor 3D representation

of the city and urbanmetrics radar-chart

TUI TableLego bricks representing

city configuration andother UI elements

Portable Computerfor calculating the urban

metrics and visualizations

Webcamlooking down atthe mirror

Surface LEDto illuminate the color tags beneath the Lego bricks

Mirrorto reflect the color tags

6

themselves autonomously (Grignard and Drogoul 2017).

Entities and behaviors are explicitly represented in a

program that iterates over several steps before the final

result. A specific ABM module capable of determining accu-

mulated traffic volume and waiting time by location has

been integrated into CityMatrix.

Inspired by the Persuasive Electric Vehicle (PEV) project

(2013-present) (MIT, n.d.) by Michael Lin from the City

Science group at the MIT Media Lab, the traffic simu-

lation models the traffic volume and user wait-time in a

city district, assuming all trips are performed by a highly

efficient autonomous shared-mobility system composed

of a fleet of PEVs. The input of the simulation is a 16 x 16

matrix of the city grid. Each cell in the city grid can be either

a building with a specific number of people living or working

in it (building population), an empty lot, or a segment of a

road. The building population drives the generation of trip

requests during a one-day cycle in the simulation. Similar

to a shared-mobility system such as Uber, the nearest

available PEV would pick up the person requesting trans-

portation, travel, and drop him or her off at the required

destination. The system logged the accumulated traffic

2 TUI Table with Lego brick modules, projections, sliders, toggles, and a vertical display screen.

3 Users to change the layout of land-use by moving opti-cal-tagged modules.

4 Users can change building heights and urban density by manipulating the building height slider.

5 Hardware structure of CityMatrix labeled with the main components.

6 A view of the optical-tagged Lego bricks from beneath the table.

7 Software structure of CityMatrix.

7

volume and user wait-time on each road cell for the period

of a one-day cycle in the simulation. The output of this

traffic simulation was a 16 x 16 matrix of which each road

cell contained both value of the traffic volume and wait-

time (Figure 8). The focus of the study is the methodology

by which ML prediction could facilitate real-time feedback,

but not the fidelity of the simulation. For future practical

projects, the the ABM should be calibrated and verified with

real-world data.

Solar simulation was done using DIVA (Kröner et al 1990).

The goal was to quantify the full year solar radiation

recieved on each building's rooftop and in each courtyard.

Batch Simulation for Training Dataset

In order to train a real-time machine learning prediction

model for traffic simulation, a training dataset containing

at least 10,000 instances of traffic simulation results

is necessary to reach enough prediction precision. We

randomly generate 10,000 different city grid configura-

tions. A batch process in GAMA takes multiple input city

JSON configuration files, runs a traffic simulation model

one by one, and provides JSON city files for each road cell.

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8

8 Example of the traffic ABM mid-simulation. White dots represent PEVs, and the heatmap represents traffic volume. Blue/Green/Red = Low/Med/High.

9 Architecture of the three-layer CNN predictor.

The JSON object contains simulation results of both traffic

volume and wait-time. The simulation of one city configura-

tion takes about 1 to 5 minutes. All simulation tasks were

distributed to eight computers, and completing the 10,000

simulations took 18 hours. Similarly, we constructed a

batch controller in Rhino Grasshopper to simulate the same

10,000 city configurations for solar radiation simulations.

ML Prediction

The 10,000 city configurations were generated with

CityGenerator and simulated in GAMA and DIVA. 7,000

were used as a training set and 3,000 used as a test set

for validation. Multiple machine learning models were

compared and evaluated, including linear regression imple-

mented with Scikit-learn and a three-layer convolutional

neural network (CNN) (Niepert, Ahmed, and Kutzkov 2016)

implemented with TensorFlow (Abadi et al 2016) and Keras

(Chollet 2017) (Figure 9). Our CNN provided the most signif-

icant R2 and visual qualitative results when compared with

the ground truth from the simulations. Different parame-

ters and input feature combinations were tested for each

ML algorithm to achieve the best R2 result without overfit-

ting to our training set.

In terms of inputs and outputs, the input to each model

was the city matrix as a 16 x 16 x 2 tensor of numerical

values. For each location on the grid, we have two ground

truth scores from the GAMA simulation: (1) the traffic sum

on that location for a 24-hour long simulation, and (2) the

accumulated wait time on that location for the same period.

Beyond the GAMA simulation, we also sought to model

solar radiation levels across a city using the same machine

learning methods, but with different tuned weights and

parameters. We show the results of this approach later in

the results section.

9

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10 Comparison of the traffic volume for the original ABM result (upper) and the ML predicted output (lower) of the same city configuration, for our different cities.

11 Comparison of the waiting time for the original ABM result (upper) and the ML predicted output (lower) of the same city configuration, for our different cities.

12 Comparison of the solar radi-ation simulation result (a) and three ML prediction results (b, c, d) in both the 3D view (upper) and the 2D top view (lower)

The architecture of the CNN contained three convolution

layers. A shallow CNN is effective here due to the small data

input size (16 x 16 x 2) and smaller dataset size. For more

complex city configurations with larger grid sizes, a deeper

and wider CNN may be more suitable.

Results

After training our models and tuning parameters to achieve

the best possible accuracy, we sought to evaluate their

performance on the validation set of 3,000 cities and

also to take note of how the models performed when they

were deployed into the CityMatrix ML server architec-

ture described above. With Linear Regression, the best R2

achieved was 0.571. With CNN, the best R2 achieved was 0.86.

Figure 10 and Figure 11 are comparisons of the GAMA

traffic simulation results (upper) and the machine learning

predictions (lower) of both the traffic volume heat-map

and the wait-time heat-map respectively in four different

city examples. Figure 12 shows the comparison of the

solar radiation simulation result (a) and three ML predic-

tion results (b, c, d). The prediction successfully kept the

features of the simulation intact that were pertinent to

user decision making. Beyond the numerical performance

of these algorithms from a data standpoint, we also seek

to ensure a fast computation time for users who work

with the CityMatrix human-computer interface (HCI). The

CNN could be run on an input city configuration in under

10 milliseconds, as opposed to the ABM model which took

more than 1 minute.

APPLICATIONSReal-time Feedback

We applied our technique as an integral part of the

CityMatrix project, which is designed to facilitate public

engagement with multiple stakeholders, both profes-

sional and nonprofessional. Stakeholders can rapidly and

collaboratively explore urban configurations without prior

knowledge by making simple, iterative moves. For instance,

Figures 13 and 14 show the heat-maps that CityMatrix

provides as real-time feedback.

In order to supply users with relevant feedback to guide

their decision making, a real-time system for calculating

metrics of the city configuration was needed. While our

traffic ABM was effective, it takes too long between moves

to calculate the traffic of an altered configuration. Our CNN

allowed for move-by-move calculations that facilitated

discussion and exploration. Compared with conventional

tools, where the human users need to act on their own most

of the time with analytics only appearing after long compila-

tion periods, our technique allowed for consistently guided

decision-making.

Optimization and Design Recommendations

In order to create the best urban planning tool, we knew

we needed to develop a clear human–computer interaction

platform. Humans are skilled at subjective value judg-

ments such as culture, aesthetics, and emotion, whereas

machines are not. However, machines are capable of

handling complex numeric calculations with multiple

objectives simultaneously with efficiency and precision. To

combine the best attributes of the human and the machine,

we used our real-time analysis capabilities to design an

option space search AI for CityMatrix.

After users made a change to the city, the server performed

a search over the possible moves from that state to opti-

mize the city based on user objectives (Figure 15). Users set

sliders to determine which metrics they wanted to optimize

for, and the position of these sliders determined the weights

for each metric. A linear combination of the metrics mulit-

plied by their weights produced a single value that allowed

for two cities to be compared. By analyzing potential

12

run time: 2.2 minutes run time: 0.2 milliseconds run time: 0.5 milliseconds run time: 0.4 milliseconds

a b c d

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13

14 15

changes, the system is able to suggest the best possible

moves based on values from multiple cities that are one or

more moves away from the system's current city. Then the

best option can be selected based on its value.

In the first iteration of CityMatrix, we performed a simple

random search over possible next moves and selected

the most optimal one. Further iterations could use more

advanced methods such as Monte Carlo Tree Search

(MCTS) (Browne et al. 2012). This would allow for optimizing

for multiple moves, so that even though the user would still

only see one suggested move, they would be guided away

from suboptimal options. To facilitate deeper searches,

we developed an asynchronous approach where the

suggested move would only update once it was complete,

instead of synchronously on each user input.

The total number of the possible moves (search space)

from any given city configuration was 1,966 (16 x 16 x 7

for changing a building cell plus 6 x 29 for changing the

building height of one type). For such a small search space,

150 to 500 possible moves were randomly chosen and

evaluated. It took one CPU thread less than one second to

evaluate 150 possible moves.

EVALUATIONTo understand and evaluate the user-interface and the

functionality of the optimization suggestions, five pilot-

user tests were conducted. Each group had four users

from both professional and non-professional backgrounds

related to urban decision-making (Figure 16). Server data

and questionnaire answers were collected to analyze the

usability of CityMatrix.

Server Data Analysis

The server logged data points constantly when there was

new user input. Each data point included the current state

of the building, type ID on each grid cell, the building height

(building population), the heat-map value of the five aspects

of each grid cell, the urban performance metrics on the

radar-chart, the next move suggested by the AI, and the

five weights of the AI assistance. With the collected serv-

er-logged data, the urban performance metrics of five

aspects and the total score evolving in each round was

reconstructed. Figure 17 shows the data of one typical user

test. The x-axis represents the scale of time in minutes,

while the y-axis represents the normalized score. In Round

1, the experiment was conducted without the optimization

suggestion function. In Round 2, the users were provided

with the suggestions from the system. Insights about the

process were revealed by the chart and the video and audio

recordings. In the pattern found on the chart, optimization

suggestions helped stabilize and improve the total score in

Round 2 compared to Round 1.

Questionnaire Analysis

Questionnaire data provided a perspective to some of the

qualitative aspects about the usefulness of the system.

According to the answers of the questionnaire, we find that

most of the users agree that the user interface is overall

easy to understand, the recommendations made by the AI

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13 Urban performance heat-map: traffic performance.

14 Urban performance heat-map: solar access performance.

15 Orange markers and arrows on the table indicate the suggested next move (upper); Orange polyline and texts beside the scores indicate the projected score changes if accepting the AI suggestion (lower left); Orange arrow in the 3D city view indicate the suggested next move (lower right).

16 20 users participated in five user tests in evaluation of CityMatrix.

16

are helpful, and the CityMatrix system promotes collabora-

tion in urban decision-making.

CONCLUSION Contribution CityMatrix was designed as a first step towards evidence-

based and democratic decision making. It promoted

collaborations among a wide range of stakeholders and a

potential solution to enhance the accessibility and efficiency

of public engagement events. This reduces the delay costs

and improves the design quality.

Real-time simulation feedback was not in demand because

the proper collaboration and public engagement has not

yet been emphasized and addressed. The research in the

City Science group such as the CityScope project opened

up new opportunities to innovatively address these issues.

To facilitate a more informative urban public engage-

ment tool, real-time feedback is necessary. The real-time

feedback is not only important for public accessibility, but

also to enhance the quality of decision-making and design

processes. With real-time feedback, the user can examine

the spectrum of design variations in a short amount of time.

This transforms a quantitative calculation into design intu-

ition. In this work, a versatile, quick, accurate, and low-cost

method to enable real-time feedback of multiple complex

simulations for stakeholders was explored and deployed.

Instead of running these complex simulations in real-

time, which would have been impossible given the massive

resources required, the system predicts a simulated result

with a pre-trained machine learning algorithm in real-time.

Cities are extraordinarily complex. To enable people to navi-

gate, understand, and interact with complex information

and possible solutions, the advanced optimization search

algorithm was developed to provide recommendations on

a step-by-step basis. The optimization suggestions freed

stakeholders from excessive quantitative considerations

and enabled them to focus on the qualitative ones. As a

result, the quality of the decision was improved by taking

advantage of the organic combination of both human intelli-

gence and machine intelligence.

Future Work

The current version of CityMatrix and the optimization

suggestions inspire further thinking, refinement, and

improvement of the project. Some potential directions for

future work include:

• We can apply the system to a real context, using real-

time data, and solving a real community issues.

• The system can not only give suggestions, but also

inform the users as to why that decision was made.

• CityMatrix could incorporate more aspects of urban

simulations.

• A parallel process can enable the original urban

simulations to run simultaneously, supporting both

the preliminary and final stage of the decision-making

process. The real-time, rapid prediction of the simu-

lation provides enough precision for an effective

decision-making process. Meanwhile, the system can

continue calculating the accurate, high-resolution simu-

lation solutions to confirm the final decision.

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17 Server log data visualization: Total score (thick black) vs. five urban metrics, in which, user worked without the AI assistance in Round 1 and with the AI assis-tance in Round 2.

• A renewable training dataset for machine learning can

be explored. The parallel simulation results could be fed

into the ML training dataset to improve the precision of

the ML prediction. These new data entries can increase

the precision of the ML prediction, because they are

more similar to the future user input compared to

randomly generated city configurations.

• To promote the usage of CityMatrix at scale, more open-

source work can be done, including documentation,

tutorials, and community development.

• ABM and other simulation can be validated using real-

world data.

Global Deployment and Potential Impact

CityMatrix can be used and re-developed by profes-

sionals and non-professionals globally. Earlier versions

of CityMatrix have already been used in Dubai, Hamburg,

and Andorra (Grignard 2018). It was also used as primary

research platform in workshops collaborating with Tongji

University in Shanghai (Zhang and Larsen 2018), Aalto

University in Helsinki, and in a City Science course at the

MIT Media Lab in Cambridge (Zhang et al. 2018, Alonso et

al. 2018).

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IMAGE CREDITSAll photos, drawings, and images by the authors.

Yan Zhang (Ryan) is a PhD researcher in City Science research

group at the MIT Media Lab. His current focus is developing and

deploying CityScope – an AI-enabled urban decision support

system that democratizes the urban decision-making process. He

has a background in architecture design with a special emphasis

on computational design for more than ten years. He holds a

Master of Science in Advanced Architectural Design from Columbia

University. He worked as an architect for Skidmore Owings &

Merrill LLP (SOM) and von Gerkan, Marg und Partner (GMP). His

architecture practice includes parametric form-finding and archi-

tectural design of Shanghai Oriental Sports Center.

Arnaud Grignard is a computer scientist specialized in complex

systems modelling and information visualization. He holds a PhD in

Computer Science from l'université Pierre et Marie Curie - UPMC.

He is now Research Scientist at the City Science research group at

the MIT Media Lab. While working on different fields of application

such as multi-level urban systems and human mobility, he devel-

oped a new approach called agent-based visualization to handle

real-time visualization tasks applied both to data and simulation

outputs.

Alexander Aubuchon is an undergrad student at the College

of Computer and Information Science (CCIS) at Northeastern

University while contributing to this research.

Kevin Lyons is an undergrad student at the department

of Electrical Engineering and Computer Science (EECS) at

Massachusetts Institute of Technology while contributing to this

research.

Kent Larson directs the City Science group at the MIT Media

Lab. His research focuses on developing urban interventions that

enable more entrepreneurial, livable, high-performance districts

in cities. To that end, his projects include advanced simulation and

augmented reality for urban design, transformable micro-housing

for millennials, mobility-on-demand systems that create alterna-

tives to private automobiles, and Urban Living Lab deployments in

Hamburg, Andorra, Taipei, and Boston.

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