API Changes - December 18, 2025¶

This document summarizes API changes, new layers, and updates for app developers.

Summary¶

New endpoint field: /api/v1/layers now returns registry version and updated date
New layer: michigan-congressional (13 districts)
Updated layers: All Michigan layers now use official MICRC redistricting data
Total layers: 4 (was 3)

API Changes¶

GET /api/v1/layers¶

New response fields: version and updated

{
  "version": "1.0",
  "updated": "2025-12-18",
  "count": 4,
  "layers": [
    {
      "id": "federal-congressional",
      "name": "U.S. Congressional Districts",
      "description": "119th Congress (2025-2027)",
      "scope": "federal",
      "state": null,
      "feature_count": 441
    },
    {
      "id": "michigan-state-house",
      "name": "Michigan State House Districts",
      "description": "Michigan State House districts (110 total) - MICRC 2021 final redistricting",
      "scope": "state",
      "state": "MI",
      "feature_count": 110
    },
    {
      "id": "michigan-state-senate",
      "name": "Michigan State Senate Districts",
      "description": "Michigan State Senate districts (38 total) - MICRC 2021 final redistricting",
      "scope": "state",
      "state": "MI",
      "feature_count": 38
    },
    {
      "id": "michigan-congressional",
      "name": "Michigan Congressional Districts",
      "description": "Michigan Congressional districts (13 total) - MICRC 2021 final redistricting",
      "scope": "state",
      "state": "MI",
      "feature_count": 13
    }
  ]
}

Use cases for version/updated: - Cache invalidation: Compare updated with last fetch - Display "Data as of" in UI - Detect when new layers are added

New Layer: michigan-congressional¶

Michigan's 13 Congressional districts from the official MICRC redistricting.

Endpoints:

GET /api/v1/layers/michigan-congressional
GET /api/v1/layers/michigan-congressional/features
GET /api/v1/layers/michigan-congressional/features/{district_id}
GET /api/v1/layers/michigan-congressional/geojson

Feature ID format: 2-digit padded string (01, 02, ... 13)

Sample feature:

{
  "id": "01",
  "name": "Congressional District 1",
  "properties": {
    "district": "1",
    "districtn": 1,
    "namelsad": "Congressional District 1",
    "district_id": "01",
    "state": "MI",
    "statefp": "26"
  },
  "geometry": { ... }
}

Note: This layer contains only Michigan districts. For all 441 U.S. districts, use federal-congressional.

Updated Layers¶

michigan-state-house¶

Source changed: Michigan GIS Open Data → MICRC

Field	Before	After
Source	Michigan GIS Open Data	MICRC
ID Field	`name`	`district_id`
Name Field	`label`	`namelsad`

Breaking change: Feature IDs changed format. - Before: "80", "110" - After: "080", "110" (3-digit padded)

Migration:

// Before
const feature = await fetch('/api/v1/layers/michigan-state-house/features/80');

// After
const feature = await fetch('/api/v1/layers/michigan-state-house/features/080');

michigan-state-senate¶

Source changed: Census TIGER/Line → MICRC

Field	Before	After
Source	Census TIGER/Line 2024	MICRC
ID Field	`sldust`	`district_id`
Name Field	`namelsad`	`namelsad`

Feature ID format: 3-digit padded string (001, 002, ... 038)

Layer Registry¶

Current Layers (v1.0)¶

Layer ID	Scope	State	Features	Source
`federal-congressional`	federal	-	441	Census TIGER/Line 2024
`michigan-state-house`	state	MI	110	MICRC 2021
`michigan-state-senate`	state	MI	38	MICRC 2021
`michigan-congressional`	state	MI	13	MICRC 2021

Database Files¶

data/layers/
├── registry.json
├── federal/
│   └── congressional_119.duckdb    # 441 districts
└── mi/
    ├── house.duckdb                # 110 districts
    ├── senate.duckdb               # 38 districts
    └── congressional.duckdb        # 13 districts

Common Properties¶

All Michigan MICRC layers share these properties:

Property	Type	Description
`district`	string	District number (unpadded)
`districtn`	number	District number (numeric)
`district_id`	string	Padded district ID (feature key)
`namelsad`	string	Full district name
`shape.starea()`	number	Area in square feet
`shape.stlength()`	number	Perimeter in feet

Code Examples¶

Fetching Layer List with Version Check¶

async function checkForUpdates(lastKnownUpdate) {
  const response = await fetch('/api/v1/layers');
  const data = await response.json();

  if (data.updated !== lastKnownUpdate) {
    console.log(`Registry updated: ${data.updated}`);
    // Invalidate caches, refresh layer list
    return { updated: true, layers: data.layers };
  }
  return { updated: false };
}

Loading Michigan Layers¶

// Get all Michigan layers
const response = await fetch('/api/v1/layers');
const { layers } = await response.json();
const michiganLayers = layers.filter(l => l.state === 'MI');

// Load each as GeoJSON for MapLibre
for (const layer of michiganLayers) {
  const geojson = await fetch(`/api/v1/layers/${layer.id}/geojson`).then(r => r.json());
  map.addSource(layer.id, { type: 'geojson', data: geojson });
}

Layer Switcher UI¶

// Build layer selector from API
async function buildLayerSelector() {
  const { version, updated, layers } = await fetch('/api/v1/layers').then(r => r.json());

  const select = document.getElementById('layer-select');
  select.innerHTML = '';

  // Group by scope
  const federal = layers.filter(l => l.scope === 'federal');
  const state = layers.filter(l => l.scope === 'state');

  if (federal.length) {
    const group = document.createElement('optgroup');
    group.label = 'Federal';
    federal.forEach(l => {
      const opt = document.createElement('option');
      opt.value = l.id;
      opt.textContent = `${l.name} (${l.feature_count})`;
      group.appendChild(opt);
    });
    select.appendChild(group);
  }

  if (state.length) {
    const group = document.createElement('optgroup');
    group.label = 'State (Michigan)';
    state.forEach(l => {
      const opt = document.createElement('option');
      opt.value = l.id;
      opt.textContent = `${l.name} (${l.feature_count})`;
      group.appendChild(opt);
    });
    select.appendChild(group);
  }

  // Show version info
  document.getElementById('data-version').textContent = `v${version} (${updated})`;
}

Data Sources¶

MICRC (Michigan Independent Citizens Redistricting Commission)¶

All Michigan layers now use official MICRC 2021 final redistricting boundaries.

ArcGIS REST Services: - Base: https://gisagocss.state.mi.us/arcgis/rest/services/CSS/CSS_MDOS_MICRC_Final/MapServer - Congressional: /17 - State Senate: /16 - State House: /15

Web Viewer: https://www.arcgis.com/apps/webappviewer/index.html?id=5e383a06df1d4c44a222a8d442534ebb

Census TIGER/Line¶

Federal congressional districts use Census Bureau boundaries.

URL: https://www2.census.gov/geo/tiger/TIGER2024/CD/

Changelog¶

2025-12-18¶

Added version and updated fields to /api/v1/layers response
Added michigan-congressional layer (13 districts)
Updated michigan-state-house to MICRC source (110 districts)
Updated michigan-state-senate to MICRC source (38 districts)
Changed Michigan feature ID format to padded strings

2025-12-17¶

Added michigan-state-senate layer (Census source)
Added michigan-state-house layer (Michigan GIS Open Data)

2025-12-16¶

Initial multi-layer API release
Added /api/v1/layers/* endpoints
Created federal-congressional layer