This project was caused by the need to draw the edges of the counties of Romania on a web map (Leaflet on OpenStreetMap / Mapbox). For that the only open data source I found is the poligon county limits, which is extremely detailed, including about 25K points per county. Which is great, but quite heavy to load through the internet (11MB) and to render on a dynamic map.

So here comes the first need: create sets of data that allow rendering Romania's counties with less precision, but a lot greater flexibility. Ideal: about 30 points per county.

Another need was to find the place were it would be optimal, from the user's point of view, to place a label on a county. For this, one solution would be to compute the geometrical center of the polygon. (Later I found out that, having the polygon shape, you can use Leaflet for this, so no need for math :/)

See simplified GeoJSON in the data_processing/results folder.

You need a local web server to run the project. I already had PHP on my machine, so I ran

$ cd web
$ php -S localhost:8080

in the web subfolder, and see the results in the browser at localhost:8080

$ cd data_processing

Step 1: from full contours, get information about which contour parts overlap between counties. On my machine, it took around 30 minutes:

$ ruby find_common_contours.rb data/contours-full.geojson  > data/common-contours.json

The resulting information is a JSON serialized hash (keys: county codes, values: arrays(first position: an index range, second position: the neighbour county code))

Step2: from full contours, and the information about borders between counties, generate a GeoJSON with simplifed contours:

$ ruby simplify_contours.rb data/contours-full.geojson data/common-contours.json > data/contours-simplified.geojson

You can play with the parameters (tolerance, border_tolerance, high_quality, precision) to tweak the result to lower or higher fidelity.

Optional: Step3: from the simplified GeoJSON, generate a basic JSON (that is a lot smaller, and is used in the web app):

$ ruby geojson_to_minified_json.rb data/contours-simplified.geojson > data/contours-simplified.json

Simplified contours, raw JSON (31K):

Simplified contours GeoJSON (112K):

Original GeoJSON (11MB):

Simplify counties - done

• and saved data for a conveninent simplification tolerance and floating point precision

Determine county center - done (and removed; it's implemented in Leaflet.js)

Other features

• geometrical center shown as a county name label
• county capital shown as a less visually appealing circle, on click you see the city name
• country regions are assigned a color (in such a way as all neighbouring regions have different color)
• counties colored in different shades of region's color

Contour segment simplification: SimplifyRb, a Ruby port of simplify.js by Vladimir Agafonkin

Overall data processing: thanks to Rodica Pintea, my highschool computer science teacher, that ispired me to love algorithms and programming

Thanks to DigitalOcean, for organizing HacktoberFEST, which gave me the extra push to do science for good.