October 20, 2014

Using GeoTools with Multiple User Accounts

I have a situation where I have multiple GeoTools applications being run on a server by different users. I was having a lot of issues with exceptions about not being able to decode CRS codes, even though I was sure I had the gt-epsg-hsql file included in my JAR, and had set up Maven correctly to include the dependency. It turns out the issue was that the gt-epsg-hsql extracts its hsql database of projections to Geotools in the system temporary directory, and if there are multiple geotools apps running as different users, the first one to start gets the directory, and the remaining ones crash because they don’t have permissions to access it.

August 10, 2014

Running RStudio Server on Amazon EC2

R is a great environment for statistical computing; I’ve used it in a number of projects. RStudio is hands-down the best IDE for R (there is even less debate here than there is about emacs being the best editor). Sometimes, though, I find that I need to run analyses that require more computing power than my personal computer can provide (especially since my desktop is currently in storage in California and I’m in Illinois with a circa-2007 netbook with 2GB of RAM).

May 1, 2014

Predicting the Popularity of Bicycle Sharing Stations: An Accessibility-Based Approach

I presented a paper about modeling the popularity of bikesharing stations at the California Geographical Society 2014 annual meeting in Los Angeles. I calculated accessibility measures to jobs and residents using Census and OpenStreetMap data and the open-source OpenTripPlanner network analysis suite. I used those as independent variables in regressions to try to explain the popularity of bikesharing stations. I used bikeshare popularity data from Washington, DC, San Francisco, and Minneapolis–St.

April 24, 2014

Identifying Patterns in Bikeshare Trip Making

Bay Area Bike Share has recently released their trip history data; the data file contains the origin station, end station, time and date, and user type (day-pass or subscriber) for all the trips taken on the system since its inauguration on August 29, 2013. For another project, I had calculated accessibility measures for each bikeshare station in the Bay Area Bike Share system (using the beta OpenTripPlanner transportation analysis suite; see this post and the attached paper).

March 26, 2014

Overanalyzing Board Games: Network Analysis and Pandemic

I like board games, and one of my favorites is Pandemic. The game consists of a board (pictured above) with a world map on it, with various cities highlighted, and a network between the cities. Disease breaks out randomly in the cities at the start of the game (using the shuffled infection deck) and then progresses using the same deck. Players cooperatively attempt to quell disease by moving between cities and treating disease.

February 22, 2014

Visual Correlation Matrices

Correlation matrices show up often in papers and anywhere data is being analyzed. They are useful because they succinctly summarize the observed relationships between a set of variables; this also makes them very good for exploratory data analysis. However, correlation matrices by themselves are still a bit difficult to interpret, as they are simply numbers. For example, here is the output of the R cor() function. There’s a lot of useful information there, but it’s still a bit difficult to interpret.

December 28, 2013

Schelling's Segregation Model in JavaScript

Schelling’s segregation model is an interesting model of neighborhood dynamics developed by the economist Thomas C. Schelling. It’s an agent based model, in which agents of two groups (which could be based on income, political affiliation, race, &c.) are placed on a grid. There is some threshold for what percentage of an agent’s neighbors must be of the same group for it to be happy. For instance, agents might want 30% of their neighbors to be of the same group.

December 14, 2013

Analyzing the Effects of Space and Time on Bikeshare Use

Bikeshare systems have been taking off in the US of late. One of the first of these systems, Capital Bikeshare in Washington, DC, has been in operation since 2010. The automated bikeshare stations generate a wealth of information; the start and end stations and times of each trip are recorded, and are available to the public in anonymous form. This project used the approximately 4.5 million trips taken on the system from the fourth quarter of 2010 until the second quarter of 2013.

June 20, 2013

Microaccessibility with OpenTripPlanner

Analysis of accessibility is generally undertaken in large regions, such as metropolitan areas or entire countries. Frequently it also uses macro temporal scales, as in before-and-after analysis. This analysis instead looks at micro scales, both spatial and temporal. The study area is the University of California, Santa Barbara campus and the adjoining student community of Isla Vista. I analyzed accessibility at every hour of a typical week, so that accessibility can be compared at different times of day and on different days.

April 26, 2013

Jane Jacobs and Global Cities Presentation at the California Geographical Society

I gave a presentation on the connections between Jane Jacobs and Global Cities Theory at the California Geographical Society 2013 conference. The slides from the presentation are on the Publications page.