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Tile Servers & Basemaps Guide

Free tile services, self-hosting for resilience, custom map styling with Maputnik, and offline tile caching for field operations.

Why Basemaps Matter

The basemap provides vital geographic context for overlay data like enforcement zones and detention centers. Proprietary basemap providers introduce unacceptable risks:

Risk Impact
Unexpected costs API pricing changes
Rate limiting Traffic spikes blocked
User tracking Location data harvested
Reliability Downtime during critical events

Open-source and self-hosted tile services eliminate these risks.

Free Public Tile Services

OpenStreetMap-Based Services

Service URL Pattern Use Case
OSM Standard {s}.tile.openstreetmap.org/{z}/{x}/{y}.png General purpose
Humanitarian tile-{s}.openstreetmap.fr/hot/{z}/{x}/{y}.png Crisis response
Carto Light {s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png Minimal, clean
Carto Dark {s}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}.png Dark mode

Usage Requirements

Mandatory Attribution:

© <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors

Usage Limits

Service Limit Notes
OSM Fair use No bulk downloading
Carto 75,000/month free Requires signup for more
Stamen Fair use Migrated to Stadia Maps

Self-Hosting for Resilience

Why Self-Host?

  • No rate limits - Handle traffic spikes during raids
  • Privacy - No third-party IP logging
  • Reliability - Control your uptime
  • Customization - Full style control

Software Stack

Component Software Purpose
Tile Server TileServer GL Serve vector/raster tiles
Data Source OpenMapTiles Pre-processed OSM data
Styling Maputnik Visual style editor

Hardware Requirements

Scope CPU RAM Storage
Regional (single state) 2 cores 2GB 10GB SSD
National (USA) 4 cores 8GB 50GB SSD
Global (dynamic rendering) 4+ cores 16GB+ 100GB+ SSD

Docker Deployment

# docker-compose.yml
version: '3'
services:
  tileserver:
    image: maptiler/tileserver-gl
    ports:
      - "8080:8080"
    volumes:
      - ./data:/data
    command: --config /data/config.json

TileServer GL Configuration

{
  "options": {
    "paths": {
      "root": "/data"
    }
  },
  "styles": {
    "advocacy-light": {
      "style": "styles/advocacy-light.json"
    }
  },
  "data": {
    "openmaptiles": {
      "mbtiles": "usa.mbtiles"
    }
  }
}

Custom Map Styling

Why Custom Styles?

Commercial basemaps contain visual noise that distracts from advocacy content:

  • Retail points of interest
  • Dense transit networks
  • Vibrant terrain shading

Custom styles emphasize relevant features:

  • Jurisdictional boundaries
  • Highways and migration routes
  • Enforcement infrastructure

Maputnik Editor

Maputnik is a free, browser-based visual editor for MapLibre Style Specification.

Access: https://maputnik.github.io/

Style Customization Workflow

  1. Load template style (OSM Liberty, Positron)
  2. Remove unnecessary layers (POIs, transit)
  3. Emphasize boundaries (counties, states)
  4. Adjust colors for high contrast
  5. Export style.json

Advocacy-Optimized Style

{
  "version": 8,
  "name": "Advocacy Light",
  "sources": {
    "openmaptiles": {
      "type": "vector",
      "url": "https://tiles.yourserver.org/data/openmaptiles.json"
    }
  },
  "layers": [
    {
      "id": "background",
      "type": "background",
      "paint": { "background-color": "#f8f8f8" }
    },
    {
      "id": "boundary-state",
      "type": "line",
      "source": "openmaptiles",
      "source-layer": "boundary",
      "filter": ["==", "admin_level", 4],
      "paint": {
        "line-color": "#666666",
        "line-width": 1.5,
        "line-dasharray": [3, 2]
      }
    },
    {
      "id": "boundary-county",
      "type": "line",
      "source": "openmaptiles",
      "source-layer": "boundary",
      "filter": ["==", "admin_level", 6],
      "paint": {
        "line-color": "#999999",
        "line-width": 0.5
      }
    }
  ]
}

Color Accessibility

Purpose Recommended Avoid
Basemap Muted grays (#f8f8f8) Vibrant colors
Boundaries Dark gray (#666) Light gray
Overlay data High contrast (red, blue) Similar to basemap
Text 4.5:1 contrast ratio Low contrast

Offline Tile Caching

Browser-Based Caching (MapLibre)

// Using maplibre-gl-offline-ts plugin
import { OfflineControl } from 'maplibre-gl-offline-ts';

map.addControl(new OfflineControl({
  database: 'advocacy-tiles-db',
  storageType: 'indexeddb'
}));

Mobile Offline Packages

MBTiles Format

Pre-rendered tiles stored in SQLite database:

# Generate MBTiles for California
tilemaker --input california.osm.pbf \
          --output california.mbtiles \
          --config config.json

Distributing Offline Maps

Method Use Case
QR code Link to download page
Direct download Flyers with URL
USB distribution Community events

Mobile Apps Supporting Offline

App Platform Custom POI Support
OsmAnd Android/iOS ✅ GPX import
Maps.me Android/iOS ✅ Bookmarks
Organic Maps Android/iOS ✅ KML import

OsmAnd Custom POI Import

<!-- checkpoints.gpx -->
<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="advocacy-tools">
  <wpt lat="32.5" lon="-117.1">
    <name>San Ysidro Checkpoint</name>
    <desc>Permanent Border Patrol checkpoint</desc>
    <extensions>
      <osmand:icon>checkpoint_red</osmand:icon>
      <osmand:background>circle</osmand:background>
    </extensions>
  </wpt>
</gpx>

Tile Formats

Raster vs Vector

Aspect Raster Tiles Vector Tiles
Format PNG/JPG images PBF binary
Styling Fixed at generation Dynamic client-side
File size Larger Smaller
Server load Higher (rendering) Lower (static files)
Use case Simple maps Dynamic filtering

Vector Tile Advantages

  • Client-side styling - Change colors without regenerating
  • Dynamic filtering - Toggle layers instantly
  • Smaller bandwidth - Compressed geometry data
  • Crisp at all zooms - No pixelation

Performance Optimization

CDN Configuration

# nginx.conf for tile caching
location /tiles/ {
    proxy_pass http://tileserver:8080/;
    proxy_cache tiles_cache;
    proxy_cache_valid 200 7d;
    proxy_cache_key "$request_uri";
    add_header X-Cache-Status $upstream_cache_status;
}

Tile Loading Strategies

Strategy Description
Viewport-first Load visible tiles first
Progressive Low-res then high-res
Predictive Pre-load adjacent tiles

Monitoring

Track tile server health:

  • Response times
  • Cache hit rates
  • Error rates during high traffic

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