Interesting blog post.

OpenStreetMap city blocks as GeoJSON polygons

Extracting blocks within a city as GeoJSON polygons from OpenStreetMap data

I'll talk about using QGIS software to explore and visualize LARGE maps and provide a Python script (you don't need QGIS for this) for converting lines that represent streets to polygons that represent city blocks. The script will use the polygonize function from Shapely but you need to preprocess the OSM data first which is the secret sauce.

peteris.rocks/blog/openstreetmap-city-blocks-as-geojson-polygons

Summary:

• Download GeoJSON files from Mapzen Metro Extracts
• Filter lines with filter.py
• Split LineStrings with multiple points to LineStrings with two points with split-lines.py
• Create polygons with polygonize.py
• Look at results with QGIS or geojson.io

GeoJSON: geojson.io/#map=14/-14.4439/28.4334