Spatial Data Format of the Week: XYZ Tiles & Web Services (WMS/WFS/IIIF)

Web Mapping Formats

This week covers four interconnected web mapping formats:

  1. XYZ Tiles — Pre-rendered map images in pyramid structure
  2. WMS (Web Map Service) — On-demand map image rendering
  3. WFS (Web Feature Service) — Vector feature streaming
  4. IIIF (International Image Interoperability Framework) — Georeferenced historic cartography

All four enable web mapping without downloading entire datasets.

Part 1: XYZ Tiles (Slippy Map Tiles)

What it is: Pre-rendered map images organized in a pyramid folder structure based on zoom level, row, and column.

The Tile Pyramid Concept

Zoom level 0: Entire world = 1 tile (256×256 pixels)

Zoom 0:   [world.png]

Zoom 1: World = 2×2 = 4 tiles

Zoom 1:   [0,0] [1,0]
          [0,1] [1,1]

Zoom 2: World = 4×4 = 16 tiles

Each zoom level quadruples:

  • Zoom 3: 64 tiles (8×8)
  • Zoom 10: 1,048,576 tiles (1,024×1,024)
  • Zoom 18: 68 billion tiles

URL Structure

Standard XYZ tile URL:

https://tile.openstreetmap.org/{z}/{x}/{y}.png

Example: San Francisco at zoom 12

https://tile.openstreetmap.org/12/654/1582.png

Where:

  • {z} = Zoom level (0-18 typically)
  • {x} = Column (west to east)
  • {y} = Row (north to south)

Common Tile Sources

OpenStreetMap:

https://tile.openstreetmap.org/{z}/{x}/{y}.png

CartoDB Dark:

https://cartodb-basemaps-{s}.global.ssl.fastly.net/dark_all/{z}/{x}/{y}.png

{s} = subdomain (a, b, c, d) for load balancing

Stamen Terrain:

https://stamen-tiles.a.ssl.fastly.net/terrain/{z}/{x}/{y}.png

Satellite (ESRI):

https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}

Using XYZ Tiles in QGIS

Add Tile Layer:

  1. Browser Panel → XYZ Tiles → (right-click) New Connection
  2. Name: Give it a descriptive name
  3. URL: Paste tile URL template
  4. Click OK
  5. Double-click to add to map

Example Configuration:

  • Name: OpenStreetMap
  • URL: https://tile.openstreetmap.org/{z}/{x}/{y}.png

XYZ Tile Advantages

1. Speed

  • Pre-rendered = instant display
  • No processing time
  • Cached by browsers/CDN

2. Simplicity

  • Just images (PNG/JPEG)
  • Any web server can host
  • Works with simple HTTP GET requests

3. Scalability

  • CDN-friendly (CloudFlare, Akamai)
  • Parallel tile fetching (load many at once)
  • Handles millions of users

4. Universal Support

  • Every web mapping library (Leaflet, Mapbox, OpenLayers)
  • Mobile mapping apps
  • QGIS, ArcGIS Online

XYZ Tile Limitations

1. Static Content

  • Can't change what's displayed (pre-rendered)
  • Can't query attributes (just images)
  • Can't style dynamically

2. Storage Requirements

  • Full global tileset at zoom 18 = petabytes
  • Typical country-scale tileset = gigabytes to terabytes

3. Update Overhead

  • Modify one feature = regenerate all affected tiles
  • Time-consuming for large areas

4. Fixed Zoom Levels

  • Only specific zoom levels (discrete, not continuous)
  • "Jumpy" zoom experience

When to Use XYZ Tiles

Best for:

  • Basemaps (OpenStreetMap, satellite imagery, terrain)
  • High-traffic web maps (millions of users)
  • Static data (doesn't change frequently)
  • Fast display (pre-rendered performance)

Avoid when:

  • Dynamic data (real-time, frequently updated)
  • User-styled layers (custom symbology per user)
  • Vector analysis needed (tiles are images, not features)
  • Attribute queries required

Part 2: WMS (Web Map Service)

What it is: OGC standard protocol for serving georeferenced map images dynamically rendered from spatial databases.

How WMS Works

Client request:

https://example.com/geoserver/wms?
  service=WMS&
  version=1.3.0&
  request=GetMap&
  layers=counties&
  bbox=-124,32,-114,42&
  width=800&
  height=600&
  crs=EPSG:4326&
  format=image/png

Server response: Rendered PNG image of counties within bounding box.

WMS vs. XYZ Tiles

Aspect WMS XYZ Tiles
Rendering On-demand (dynamic) Pre-rendered (static)
Speed Slower (render time) Faster (cached)
Flexibility Any extent, projection, style Fixed zoom levels, style
Data updates Instant (reflects database changes) Requires tile regeneration
Storage Minimal (source data only) Large (millions of tiles)
Query support Yes (GetFeatureInfo) No (just images)

Using WMS in QGIS

Add WMS Layer:

  1. Layer → Add Layer → Add WMS/WMTS Layer
  2. Click New connection
  3. Name: Service name
  4. URL: Base WMS endpoint (without parameters)
  5. Click OK → Connect
  6. Select layers → Add

Example WMS Services:

USGS National Map:

https://basemap.nationalmap.gov/arcgis/services/USGSTopo/MapServer/WMSServer

OpenStreetMap WMS (terrestris):

https://ows.terrestris.de/osm/service?

California Data Geoportal:

https://gis.data.ca.gov/arcgis/services/...

WMS Capabilities

GetCapabilities: Query available layers

https://example.com/wms?service=WMS&request=GetCapabilities

GetMap: Fetch map image (see example above)

GetFeatureInfo: Query attributes at clicked point

https://example.com/wms?
  service=WMS&
  request=GetFeatureInfo&
  query_layers=counties&
  x=250&
  y=150&
  ...

When to Use WMS

Best for:

  • Dynamic data (real-time, frequently updated)
  • Custom rendering (user-defined styles, filters)
  • Analysis/query (GetFeatureInfo)
  • Multiple projections (server-side reprojection)

Avoid when:

  • High traffic (slow rendering under load)
  • Static basemaps (tiles are faster)
  • Offline access needed (requires server connection)

Part 3: WFS (Web Feature Service)

What it is: OGC standard for serving vector features (geometry + attributes) over the web, unlike WMS which serves images.

WFS vs. WMS

  • WMS: Serves images of maps (raster)
  • WFS: Serves features (vector data—points, lines, polygons with attributes)

Key difference: WFS returns actual geometry and attributes, enabling client-side styling and analysis.

How WFS Works

Request features:

https://example.com/geoserver/wfs?
  service=WFS&
  version=2.0.0&
  request=GetFeature&
  typeNames=counties&
  count=100&
  outputFormat=application/json

Response: GeoJSON with features:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {...},
      "properties": {
        "name": "Santa Clara County",
        "population": 1936259
      }
    }
  ]
}

Using WFS in QGIS

Add WFS Layer:

  1. Layer → Add Layer → Add WFS Layer
  2. Click New connection
  3. URL: Base WFS endpoint
  4. Click OK → Connect
  5. Select layer → Add

Result: Editable vector layer (not image) loaded into QGIS.

WFS Capabilities

GetCapabilities: List available feature types

https://example.com/wfs?service=WFS&request=GetCapabilities

GetFeature: Fetch features (with filters, bbox, attribute queries)

Transaction (WFS-T): Insert, Update, Delete features remotely

  • Collaborative editing
  • Mobile data collection apps
  • Real-time feature updates

Common WFS Sources

National GI Portal (many countries) USGS WFS Services (hydrography, boundaries) City/County GIS Portals (parcels, zoning, infrastructure)

When to Use WFS

Best for:

  • Vector analysis (need geometry, not images)
  • Attribute queries (filter by properties)
  • Editable data (collaborative mapping)
  • Client-side styling (Leaflet, Mapbox custom styles)
  • Data integration (merge remote vectors with local data)

Avoid when:

  • Large datasets (>100,000 features—too slow)
  • Raster data (use WMS or COG)
  • Display-only (WMS/tiles are faster)

Part 4: IIIF (International Image Interoperability Framework)

What it is: A set of open standards for delivering high-resolution images over the web, increasingly used for georeferenced historic maps from libraries and archives.

IIIF + Allmaps.org: Historic Cartography Pipeline

IIIF enables libraries to serve historic maps at web scale.

Allmaps.org provides georeferencing tools that create XYZ tile layers from IIIF images.

How IIIF Works

IIIF Image API delivers image tiles similar to XYZ tiles, but with flexible parameters:

Standard IIIF URL structure:

https://example.org/iiif/2/{identifier}/{region}/{size}/{rotation}/{quality}.{format}

Example:

https://dlcs.io/iiif-img/3/2/abc123/full/800,/0/default.jpg

Where:

  • {identifier}: Unique image ID
  • IIIF + Allmaps is the library archives**—historic treasures made accessible, georeferenced for modern analysis.

Key takeaway: Choose tiles for speed, WMS for flexibility, WFS for analysis, IIIF for historic cartography. Often you'll use all four in one project—tiles as basemap, WFS for analysis layers, WMS for dynamic overlays, IIIF for historical context.

See Also

Major map collections with IIIF support:

Library of Congress:

https://www.loc.gov/collections/panoramic-maps/

David Rumsey Map Collection:

https://www.davidrumsey.com/

British Library:

https://www.bl.uk/maps

Stanford Libraries:

https://searchworks.stanford.edu/view/...

Allmaps.org: Georeferencing IIIF Images

Allmaps turns IIIF historic maps into georeferenced XYZ tile layers you can use in QGIS, Leaflet, or any web map.

Workflow:

  1. Find historic map with IIIF manifest (Library of Congress, David Rumsey, etc.)
  2. Open in Allmaps Editor: https://editor.allmaps.org/
  3. Add control points (match historic map features to modern coordinates)
  4. Allmaps generates XYZ tile URL
  5. Use tile URL in QGIS or web maps

Using Allmaps Tiles in QGIS

After georeferencing in Allmaps Editor, you get a tile URL like:

https://allmaps.xyz/maps/{map-id}/{z}/{x}/{y}.png

Add to QGIS:

  1. Browser Panel → XYZ Tiles → (right-click) New Connection
  2. Name: Historic Map Name (e.g., "Sanborn 1895 SF")
  3. URL: Paste Allmaps tile URL
  4. Click OK
  5. Double-click to add to map

Result: Historic map overlays modern basemap, georeferenced and tiled.

Allmaps Features

1. Cloud-based georeferencing

  • No software installation
  • Works directly with IIIF URLs
  • Results stored in W3C Web Annotation format

2. Mask tool

  • Remove borders, legends, decorative elements
  • Clean overlay on modern maps

3. Multiple transformation algorithms

  • Polynomial: Best for most historic maps
  • Thin Plate Spline: Handles warped/distorted maps
  • Projective: For maps with perspective distortion

4. Shareable URLs

  • Each georeferenced map gets permanent URL
  • Embed in web pages or load in QGIS
  • Collaborative georeferencing

Example: Using Library of Congress Maps

1. Find map at LOC:

2. Copy IIIF Manifest URL, e.g.:

https://www.loc.gov/item/2013593069/manifest.json

3. Open Allmaps Editor:

4. Georeference:

  • Click historic map location
  • Click corresponding modern map location
  • Repeat 3-6 times (minimum 3 control points)
  • Click Results tab

5. Copy tile URL:

https://allmaps.xyz/maps/abc123def456/{z}/{x}/{y}.png

6. Add to QGIS (see workflow above)

IIIF + Allmaps Advantages

✅ No downloads: Stream historic maps from library servers

✅ High resolution: IIIF delivers full detail at all zoom levels

✅ Permanent URLs: Libraries maintain collections long-term

✅ Free access: Most institutions provide open IIIF endpoints

✅ Collaborative: Share georeferenced maps via URL

✅ Standards-based: IIIF + W3C Web Annotations

IIIF + Allmaps Limitations

❌ Requires IIIF support: Not all archives have IIIF

❌ Manual georeferencing: Must add control points yourself

❌ Internet required: Cannot work offline

❌ Variable quality: Some historic maps poorly scanned

When to Use IIIF + Allmaps

Best for:

  • Historic map overlays (Sanborn fire insurance, USGS historical topos)
  • Change detection (urban growth, coastline change)
  • Historic spatial analysis (past land use, transportation networks)
  • Teaching/research (visualizing historical geography)

Example use cases:

  • Overlay 1906 San Francisco Sanborn map over modern streets
  • Compare 1850 London map with current building footprints
  • Trace historical rail networks from USGS topos
  • Study urban expansion with sequential historic maps

Beyond Allmaps: Other IIIF Tools

IIIF Georeferencer (Klokan Technologies):

Georeferencer QGIS Plugin:

  • Connects to Georeferencer.com
  • Load georeferenced maps directly in QGIS

OpenSeadragon:

  • JavaScript viewer for IIIF images
  • Embed zoomable historic maps in web pages

Comparing Web Formats

Format Data Type Use Case Speed Flexibility
XYZ Tiles Image Basemaps, static display Fast Low
WMS Image Dynamic maps, custom styles Medium High
WFS Vector Analysis, editing, queries Slow Highest
IIIF Image Historic maps, high-res manuscripts Medium Medium
COG Raster Remote raster analysis Medium Medium

Decision matrix:

  • Need basemap? → XYZ Tiles
  • Need dynamic map rendering? → WMS
  • Need vector features for analysis? → WFS
  • Need historic maps? → IIIF + Allmaps
  • Need vector features for analysis? → WFS
  • Need remote raster processing? → COG

The Bottom Line

XYZ Tiles are the fast food of web mapping—quick, cheap, ubiquitous, but not nutritious for analysis.

WMS is the restaurant menu—custom orders, made to order, but takes longer.

WFS is the farmer's market—raw ingredients (features) for you to cook (analyze) yourself.

Key takeaway: Choose tiles for speed, WMS for flexibility, WFS for analysis. Often you'll use all three in one project—tiles as basemap, WFS for analysis layers, WMS for dynamic overlays.

See Also

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