Simon Willison’s Weblog


Scraping hurricane Irma

10th September 2017

The Irma Response project is a team of volunteers working together to make information available during and after the storm. There is a huge amount of information out there, on many different websites. The Irma API is an attempt to gather key information in one place, verify it and publish it in a reuseable way. It currently powers the website.

To aid this effort, I built a collection of screen scrapers that pull data from a number of different websites and APIs. That data is then stored in a Git repository, providing a clear history of changes made to the various sources that are being tracked.

Some of the scrapers also publish their findings to Slack in a format designed to make it obvious when key events happen, such as new shelters being added or removed from public listings.

Tracking changes over time

A key goal of this screen scraping mechanism is to allow changes to the underlying data sources to be tracked over time. This is achieved using git, via the GitHub API. Each scraper pulls down data from a source (an API or a website) and reformats that data into a sanitized JSON format. That JSON is then written to the git repository. If the data has changed since the last time the scraper ran, those changes will be captured by git and made available in the commit log.

Recent changes tracked by the scraper collection can be seen here:

Generating useful commit messages

The most complex code for most of the scrapers isn’t in fetching the data: it’s in generating useful, human-readable commit messages that summarize the underlying change. For example, here is a commit message generated by the scraper that tracks the page:

florida-shelters.json: 2 shelters added

Added shelter: Atwater Elementary School (Sarasota County)
Added shelter: DEBARY ELEMENTARY SCHOOL (Volusia County)
Change detected on

The full commit also shows the changes to the underlying JSON, but the human-readable message provides enough information that people who are not JSON-literate programmers can still derive value from the commit.

Publishing to Slack

The Irma Response team use Slack to co-ordinate their efforts. You can join their Slack here:

Some of the scrapers publish detected changes in their data source to Slack, as links to the commits generated for each change. The human-readable message is posted directly to the channel.

Bot publishing to Slack

The source code for all of the scrapers can be found at

This Entry started out as README file.