Chris Eidhof

The previous weekend I participated in Hack de Overheid (translated: hack the government), which is an event where the government and technical people come together to build apps on datasets that the government makes available. People from governmental institutions presented their datasets at the start of the day.

The day before, Kars Alfrink and I made the plan to work together on “something”, where something would be the first good idea that we would get on the day itself. After watching Tim de Haan from the Dutch national archive present his dataset with all kinds of gorgeous old maps, we made the plan to present them in a new way.

It took us a while to gather all the data, as it was spread over an XML file, a CSV file and an API. One of the things I always try to do first is to have as much data offline as possible. Instead of running one large script to do everything, I first write an extremely simple script to scrape all the data and then analyze it offline.

So we started scraping the API and downloading all the images. The images were in 500x500 format, but after a bit of URL hacking we also found a way to download them in very high resolution. Then we tried to plot all the images on a map, but we quickly found that this wasn’t a feasible option: they used very old placenames. There was a file and API available to translate these placenames to modern names, but it only worked for a very small amount of placenames. This meant we had to think of another way to present them.

Because it was already the end of the afternoon, we decided to go the easy way and group them by year, but in a very visual way. We first grouped all the maps per 50 years, and filtered out the ones with no exact year (some of them were dated “somewhere between the 16th and 17th century”). These where then grouped into half centuries. We displayed them in a treemap, showing small thumbnails of the maps in each treemap cell.

Last week, I took some more time to add zooming and tile-based loading to the app, and as it is it’s almost ready for the App Store. Check out the short video to get an idea of the app.