Control CORS settings for Sanity Asset CDN when fetching GeoJSON files

Great question about Asset CDN CORS! You've hit a known limitation with Sanity's infrastructure.

The Asset CDN CORS Limitation

According to the CORS Origins documentation, the CORS settings you configure in your Management Dashboard (Settings > API > CORS Origins) apply to the Data API but do not automatically apply to the Asset CDN. This is why you're encountering CORS restrictions when trying to fetch your GeoJSON files directly from the browser—even if you've properly configured CORS for your Data API access.

Recommended Solutions

1. Use Sanity Functions (Best Option)

Sanity Functions are the modern, recommended approach for this scenario. They're serverless functions that run on Sanity's infrastructure and can fetch your asset server-side (where CORS doesn't apply), then serve it to your frontend with proper headers.

Here's the general approach:

• Create a Function that fetches the asset URL server-side
• Have it return the GeoJSON data with appropriate CORS headers
• Call this Function endpoint from your frontend instead of hitting the Asset CDN directly

Benefits: No external hosting needed, automatic scaling, stays within the Sanity ecosystem, and you control the response headers completely.

2. Store GeoJSON as Structured Data

For smaller GeoJSON files, consider storing the JSON directly in your document schema instead of as file assets. You can use an object or json field type to store the GeoJSON structure directly in your documents.

Then query it normally with GROQ through the Data API—where your CORS settings work perfectly. This approach works well if:

• Your GeoJSON files aren't too large
• You want to query or filter based on geographic data
• You need the data to be part of your content model

3. Proxy Through Your Own Backend

If you already have a backend server, you can create an endpoint that fetches from the Asset CDN and serves to your frontend. Server-to-server requests don't have CORS restrictions, so your backend can fetch the GeoJSON and add appropriate headers for your frontend.

4. Download Parameter Workaround

While not ideal for programmatic fetching, you can use the ?dl query parameter on asset URLs to trigger downloads, though this is more suited for user-initiated downloads rather than JavaScript fetch operations.

Why Functions Are Preferred

For your use case of fetching GeoJSON dynamically, Sanity Functions provide the cleanest solution—they give you full control over headers, don't require external infrastructure, and integrate natively with your Sanity project. The Asset CDN is optimized for direct media delivery (images, videos), while Functions are purpose-built for these kinds of content transformation and delivery scenarios.

Hope this helps! Let me know which approach you end up going with.