  In this paper we develop a methodology for analyzing transportation data at
different levels of temporal and geographic granularity, and apply our
methodology to the TLC Trip Record Dataset, made publicly available by the NYC
Taxi & Limousine Commission. This data is naturally represented by a set of
trajectories, annotated with time and with additional information such as
passenger count and cost. We analyze TLC data to identify hotspots, which point
to lack of convenient public transportation options, and popular routes, which
motivate ride-sharing solutions or addition of a bus route.
  Our methodology is based on using a system called Portal, which implements
efficient representations and principled analysis methods for evolving graphs.
Portal is implemented on top of Apache Spark, a popular distributed data
processing system, is inter-operable with other Spark libraries like SparkSQL,
and supports sophisticated kinds of analysis of evolving graphs efficiently.
Portal is currently under development in the Data, Responsibly Lab at Drexel.
We plan to release Portal in the open source in Fall 2017.
