You probably want the new version of deathmapnyc, this is the first version.
To get started with the web app, run
npm install
gulp
And you should see the contents of dist dir at http://localhost:8882.
To work with the underlying data, the easiest thing to do is to cd data_processing and run a docker container with ipython/jupyter loaded on it, like so:
docker run -it -v $PWD:/root ipython/scipystack /bin/bash