100-Mile Border Zone Visualization Guide | ICE Encounter

Understanding the 100-Mile Zone

The U.S. Border Patrol operates under 1953 Department of Justice regulations granting extraordinary authority within 100 air miles of any external U.S. boundary.

What This Means

Authority	Within 100 Miles
Checkpoints	Permanent and roving
Vehicle searches	Without warrant or probable cause
Property entry	Within 25 miles of border
Reasonable suspicion	Lower standard than interior

Population Impact

Statistic	Value
Population affected	~200 million people
Percentage of U.S.	Approximately 2/3
Major cities	All coastal, border states
States entirely covered	FL, ME, NH, VT, MA, CT, RI, NJ, DE, HI

Data Sources Required

U.S. Boundaries

Source: Census Bureau MAF/TIGER

Dataset	Purpose
cb_2023_us_nation_5m	National boundary
cb_2023_us_state_5m	State boundaries
cb_2023_us_county_5m	County boundaries

Download: https://www.census.gov/geographies/mapping-files/time-series/geo/cartographic-boundary.html

Maritime Baselines

Source: NOAA Office of Coast Survey

Dataset	Purpose
Maritime Limits and Boundaries	Official territorial sea baselines
Coastal baseline data	Accurate coastline for buffering

Download: https://nauticalcharts.noaa.gov/data/us-maritime-limits-702and-boundaries.html

The Projection Problem

Why This Matters

Census boundary files use Geographic Coordinate System (GCS) - specifically WGS84 (EPSG:4326). This system uses decimal degrees, not linear units.

Critical Error: Buffering by "100" on a WGS84 layer creates a 100-DEGREE buffer, not 100 miles - producing a hemisphere-sized polygon.

Solution: Reproject First

Before buffering, convert to a Projected Coordinate System (PCS) that uses meters.

Projection	EPSG	Use Case
Albers Equal Area	5070	Continental U.S. (best for area)
US National Atlas	2163	Alternative equal area
Web Mercator	3857	If matching web tiles

QGIS Workflow

Step 1: Load Boundary Data

Layer → Add Layer → Add Vector Layer
Load Census national boundary shapefile
Load NOAA maritime baseline

Step 2: Reproject to Equal Area

Vector → Data Management Tools → Reproject Layer
Source: EPSG:4326 (WGS84)
Target: EPSG:5070 (Albers Equal Area Conic)
Output: us_boundary_5070.shp

Step 3: Create 100-Mile Buffer

100 miles = 160,934 meters

Vector → Geoprocessing Tools → Buffer
Input: us_boundary_5070.shp
Distance: 160934 (meters)
Segments: 25 (smooth curves)
End cap style: Round
Output: 100_mile_zone_raw.shp

Step 4: Handle Great Lakes

The 100-mile zone does not extend through international waters like the Great Lakes.

Load international boundary layer
Vector → Geoprocessing Tools → Clip
Clip the buffer by U.S. territory
Output: 100_mile_zone_clipped.shp

Step 5: Simplify for Web

The raw buffer has millions of vertices (every coastal inlet).

Vector → Geometry Tools → Simplify
Tolerance: 1000 meters (adjust for quality)
Check: Maintain topology
Output: 100_mile_zone_simplified.shp

Step 6: Export to GeoJSON

Right-click layer → Export → Save Features As
Format: GeoJSON
CRS: EPSG:4326 (reproject back for web)
Coordinate precision: 5 decimal places
Output: 100_mile_zone.geojson

Population Analysis

Spatial Join with Census Data

Determine how many people live within the zone:

Load Census block or tract population data
Vector → Data Management → Join Attributes by Location
Join: Census blocks to 100-mile zone
Summary: Sum population fields
Export results

Key Demographic Fields

Field	Description
TOTPOP	Total population
HISP	Hispanic/Latino population
FOREIGN	Foreign-born population

Web Display Implementation

Leaflet Example

// Load and display 100-mile zone
fetch('/data/100-mile-zone.geojson')
  .then(response => response.json())
  .then(data => {
    L.geoJSON(data, {
      style: {
        fillColor: '#ff6b6b',
        fillOpacity: 0.2,
        color: '#c92a2a',
        weight: 2
      }
    }).bindPopup(`
      <strong>100-Mile Border Zone</strong><br>
      Extended Border Patrol jurisdiction
    `).addTo(map);
  });

MapLibre Example

map.on('load', () => {
  map.addSource('border-zone', {
    type: 'geojson',
    data: '/data/100-mile-zone.geojson'
  });

  map.addLayer({
    id: 'border-zone-fill',
    type: 'fill',
    source: 'border-zone',
    paint: {
      'fill-color': '#ff6b6b',
      'fill-opacity': 0.2
    }
  });

  map.addLayer({
    id: 'border-zone-line',
    type: 'line',
    source: 'border-zone',
    paint: {
      'line-color': '#c92a2a',
      'line-width': 2
    }
  });
});

Client-Side Detection

Check if a user is within the zone without sending their location to servers:

import * as turf from '@turf/turf';

// Pre-loaded zone boundary
let borderZone;
fetch('/data/100-mile-zone.geojson')
  .then(r => r.json())
  .then(data => { borderZone = data; });

function checkIfInZone(lat, lng) {
  // All processing happens locally
  const userPoint = turf.point([lng, lat]);
  const isInZone = turf.booleanPointInPolygon(userPoint, borderZone);

  if (isInZone) {
    showWarning('You are within the 100-mile border zone');
  }

  // Coordinates never transmitted - privacy preserved
  return isInZone;
}

Visualization Best Practices

Color Choices

Element	Color	Reason
Zone fill	Semi-transparent red	Indicates restriction
Zone border	Darker red	Clear boundary
Inside label	High contrast	Legibility

Interactive Features

Toggle zone visibility
Show/hide population statistics
Click for local Know Your Rights info
Link to checkpoint locations

Legend Design

<div class="map-legend">
  <div class="legend-item">
    <span class="swatch" style="background: rgba(255,107,107,0.2); border: 2px solid #c92a2a;"></span>
    <span>100-Mile Border Zone</span>
  </div>
  <div class="legend-note">
    Extended CBP/Border Patrol jurisdiction
  </div>
</div>

File Size Optimization

GeoJSON Compression

Method	Reduction
Simplification	80-90%
Coordinate precision	10-20%
TopoJSON conversion	50-70%
Gzip compression	70-80%

TopoJSON Conversion

# Convert GeoJSON to TopoJSON
geo2topo zone=100_mile_zone.geojson > 100_mile_zone.topojson

# Simplify further
toposimplify -p 0.01 100_mile_zone.topojson > 100_mile_zone_simple.topojson

Accuracy Considerations

Buffer Precision

Factor	Impact
Projection choice	Area distortion affects distance
Coastline detail	More vertices = larger file
International boundaries	Legal nuances with Canada/Mexico

Legal Nuances

The 100-mile zone is measured from:

International land borders
Territorial sea baselines (not coastline)
Includes internal waters in some cases

Note: Consult legal experts for precise jurisdictional determinations in specific locations.

Related Resources

Checkpoint Mapping - Facility and checkpoint locations
QGIS Workflows - General data preparation
Privacy Features - Client-side location detection
Know Your Rights - Checkpoints - Rights within the zone