Why does my Leaflet map open blank for someone else?

Two usual causes. The page fetches its GeoJSON from a relative path, which a browser blocks from a `file://` origin, or the tile and Leaflet CDN URLs are `http://` inside an `https://` page and get blocked as mixed content. Publishing the folder fixes the first; switching to `https://` fixes the second.

How do I share a Leaflet map without a web server?

Publish the HTML — and any GeoJSON or image files it references — to Comma. Relative references are rewritten to the uploaded copies, so `fetch('routes.geojson')` resolves, which it cannot do from the filesystem.

Do pan, zoom and popups still work?

Yes. Comma renders report HTML with scripts enabled inside a sandboxed iframe, so Leaflet initialises, tiles load over https, and markers, popups and layer controls behave normally.

Can I use it with a tile provider that needs a key?

Yes, but the key is in the published file. Use a domain- or URL-restricted public key, never a secret one.

Can people comment on a location?

Yes. Threads anchor to the rendered content, so "this depot moved in June" stays on the map rather than in a reply-all.

Share a Leaflet map

A Leaflet map is about fifteen lines of HTML and it almost never survives being sent to someone. The file arrives, it opens, and the page is grey.

Two causes, both boring, both fatal:

The data does not load. The map fetches its features at runtime:

fetch("routes.geojson")
  .then((r) => r.json())
  .then((d) => L.geoJSON(d).addTo(map));

From a file:// origin the browser blocks that as a cross-origin request. The map object exists, the container has a height, and nothing is ever drawn — with the failure visible only in the console. See why HTML reports go blank.

The tiles do not load. An http:// tile URL or an http:// Leaflet CDN script inside an https:// page is blocked as mixed content, silently.

Publish the folder

Drop the HTML — together with the GeoJSON, any CSVs and any marker images — into Comma:

The HTML becomes the report body.
routes.geojson and the rest upload alongside it, with relative references rewritten to the uploaded copies. fetch("routes.geojson") now resolves over https://, which is the step the filesystem cannot do.
Scripts run inside a sandboxed iframe (allow-scripts, no allow-same-origin), so Leaflet initialises, tiles load, and popups, layer controls and the scale bar work.

Or generate it in a job and publish with one call:

curl -fsS -X PATCH "https://commareports.com/api/v1/reports/$REPORT_ID" \
  -H "Authorization: Bearer $COMMA_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d "$(jq -n --rawfile html map.html \
        --arg t "Service coverage — $(date -u +%F)" '{title: $t, html: $html}')"

See the API reference.

Inline the library for anything durable

<script src="https://unpkg.com/leaflet/dist/leaflet.js"></script>

is fine for a draft and a liability for a map attached to a decision — no version pin, and a third party you have no agreement with. For a map that has to render the same way next year, bundle Leaflet and its CSS into the page.

Small GeoJSON is worth inlining too: one file, nothing to fetch, nothing to break.

Keys and data

Tile providers that need a key put that key in the published file. Use a domain-restricted public key.
The features are real data. A map of customer addresses is personal data — aggregate to areas when the finding is a pattern, and set report access to private or team. See sharing & access control.

The map is where the question is

Maps get sent to people who are not going to open a repository: an operations manager, a client, a council. Anchored comments keep their question on the map — "is this catchment the new boundary or the old one?" — and the answer next to it. See commenting on HTML.

Limits

Entry HTML: 5 MB (inlined GeoJSON counts). Assets: 25 MB per file, 250 MB and 500 files total — simplify geometry with mapshaper rather than shipping full-resolution boundaries a viewer cannot perceive.
Scripts run, sandboxed — no same-origin access.
60 requests/minute per token.

Try it

Comma is free — unlimited reports, unlimited commenters, unlimited revision history.

Publish a map →