How to Resolve GeoJSON Winding Order Issues While Rendering Russian Regions with D3.js?

GeoJSON Rendering Issues with D3.js

When attempting to visualize Russian regions using D3.js, users may encounter an issue where instead of the expected region boundaries, a single large black rectangle appears on the map.

Understanding the Problem

The issue stems from the winding order of the coordinates within the GeoJSON data. GeoJSON employs Cartesian coordinates, which D3.js interprets differently due to its use of ellipsoidal math. This leads to a scenario where incorrect winding order produces a feature that encompasses the entire planet except for the target region.

Inspect the SVG paths to observe the incorrect winding order. Some paths may appear correctly drawn, while others may cover the entire globe, leaving only the intended region exposed.

Finding a Solution

To fix this, reorder the coordinates using a library like Turf.js. This is necessary because the GeoJSON contains features with both correct and incorrect winding orders.

var fixed = features.map(function(feature) {
    return turf.rewind(feature,{reverse:true});
});

Note the reverse winding order. This is due to a peculiarity in D3.js where it uses the opposite winding order specified in the GeoJSON standard.

Improving the Visualization

After resolving the winding order issue, the map will display the regions, albeit potentially small. To enhance the visualization, add a fitSize method to scale and translate the map.

This will result in a more visually appealing and usable map, as depicted in the provided image.

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