Mapcel

CSV to GeoJSON + MapLibre Converter

Overview

Mapcel is a static web application that converts CSV files containing geographic coordinates to GeoJSON format with MapLibre GL JS visualization code. All processing happens client-side in the browser.

Features

• Multiple CSV Upload: Drag-and-drop or browse to upload multiple CSV files
• Auto-Detection: Automatically detects latitude/longitude columns
• Validation: Validates coordinates and reports errors
• GeoJSON Output: Outputs in WGS84 (EPSG:4326) projection with proper CRS declaration
• Live Preview: Interactive MapLibre preview of your data
• Customization:
  • Circle color, radius, and opacity per dataset
  • Map style URL configuration
  • Min/max zoom levels
  • Enable/disable map controls
• Export: Download ZIP with GeoJSON files and MapLibre JS code

Tech Stack

• Svelte 5 - Modern reactive framework with runes
• SvelteKit - App framework with static adapter
• MapLibre GL JS - Map rendering
• PapaParse - CSV parsing
• Proj4 - Coordinate projection
• JSZip - ZIP file generation
• TypeScript - Type safety

Development

# Install dependencies
pnpm install

# Start dev server
pnpm run dev

# Type check
pnpm run check

# Build for production
pnpm run build

# Preview production build
pnpm run preview

CSV Format Requirements

CSV files must contain coordinate columns with recognizable names:

• Latitude: lat, latitude, y (case-insensitive)
• Longitude: lon, long, lng, longitude, x (case-insensitive)

Coordinates must be in WGS84 format:

• Latitude: -90 to 90
• Longitude: -180 to 180

Example CSV

name,lat,lng,population
New York,40.7128,-74.0060,8336817
London,51.5074,-0.1278,9002488
Tokyo,35.6762,139.6503,13960000

Output

The tool generates a ZIP file containing:

1. GeoJSON files (.geojson) - One per CSV, in WGS84 (EPSG:4326) projection with CRS declaration
2. MapLibre code (map.js) - JavaScript to render the map
3. README (README.md) - Usage instructions