Grid Square Map

An offline, self-hostable Maidenhead grid square map. Look up any grid square (e.g. FN92, IO91, CN92) on a world map, see its coordinates and location, and calculate the distance between two squares.

Features

• World map with Maidenhead grid overlay (field labels at world zoom, 4-char square labels when zoomed in)
• Search for a grid square by name — pans to it and shows coordinates, country, and state/province
• Click any visible square on the map to select it
• Distance calculator between two grid squares — shows km/mi and draws a line on the map
• Fully offline after initial setup — no tile server, no external APIs
• Works in any modern browser

Screenshots

• Main UI

• Search for a grid square and see its location:

• Calculate distance:

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Running Without Docker

1. Clone the repo

git clone https://github.com/hestela/grid-square-map.git
cd grid-square-map

2. Download assets

Run the setup script once to download Leaflet and the map data files:

bash setup.sh

This downloads:

• Leaflet 1.9.4 (JS + CSS + marker images)
• Natural Earth 110m countries GeoJSON (~839 KB) — base map
• Natural Earth 10m states/provinces GeoJSON (~39 MB) — country/state lookup

Requires curl and bash.

3. Serve the app

Any static file server works. The simplest option:

python3 -m http.server 3456

Then open http://localhost:3456.

Other options:

# Node.js (npx, no install required)
npx serve .

# PHP
php -S localhost:3456

Note: The app must be served over HTTP — opening index.html directly via file:// will not work because the browser blocks fetch() requests for local files.

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Running With Docker

The Docker image downloads all assets at build time so no setup script is needed.

Pull from GitHub Container Registry

docker pull ghcr.io/hestela/grid-square-map:latest
docker run -p 3456:80 ghcr.io/hestela/grid-square-map:latest

Then open http://localhost:3456.

Build locally

docker build -t grid-square-map .
docker run -p 3456:80 grid-square-map

Maidenhead Grid System

Grid squares use the Maidenhead Locator System used in amateur radio:

Length	Example	Coverage
2 chars (field)	CN	20° × 10°
4 chars (square)	CN92	2° × 1°

This app supports both 2-char and 4-char locators.

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Data Sources

• Natural Earth — country and state/province boundaries (public domain)
• Leaflet — map library (BSD 2-Clause)