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Frequently Asked Questions

Why the wrapper?

The PDOK geoservices are really cool, but geospatial data and services are special and complicated. The wrapper sits between your browser and the upstream services: it accepts simple W,S,E,N bounding boxes, handles CRS reprojection (everything comes back in WGS 84), proxies around missing CORS headers, and turns WFS features into Linked Data — every feature gets a dereferenceable URI with GeoJSON-LD, RDF/XML, and Turtle representations, queryable via SPARQL.

Which services are wrapped?

• BAG WFS (buildings, dwellings, addresses)
• Kadastralekaart WFS (cadastral parcels)
• CBS wijken en buurten WFS (statistical areas)
• PDOK Locatieserver (place-name search, at pdok)
• TOP10NL / luchtfoto / AHN WMS (map backgrounds)

See the start page for clickable examples and the interactive map.

What is the bbox format?

Bounding boxes use the format W,S,E,N in decimal degrees (EPSG:4326, lon/lat). The wrapper translates to whatever axis order and CRS the upstream service expects, and always returns GeoJSON in WGS 84. If you need the raw upstream GML in its original CRS, use the .gml suffix.

Why are WMS images limited in size?

Upstream PDOK WMS services impose a maximum image dimension of 2500 px; the wrapper respects this limit. Each pixel covers bbox width / pixel width of ground — for full resolution, request a smaller bounding box or split it into tiles.

Why do I see 429 Too Many Requests errors?

To protect upstream services from excessive load, rate limiting is in place: each IP address may make 50 requests per 10 minutes. The allowance refills continuously, so after hitting the limit you regain roughly one request every 12 seconds. Requests over the limit receive HTTP status 429.

Registered heavy users can bypass the limit with an API key, sent as an HTTP header:

Authorization: Bearer <your-api-key>

Contact the operator (see below) to request a key.

How do I access older data (temporal access)?

Time-changing resources — WMS layers with a time dimension and TIME-capable WFS services — support Memento (RFC 7089) temporal negotiation. A /wms or /wfs URI is the original resource (latest data) and acts as its own TimeGate: send an Accept-Datetime: Thu, 25 Jun 2020 12:00:00 GMT header and the wrapper replies 302 to the corresponding memento — the same URI with a time= component identifying a 30-day window ending at the requested date. time= is memento URI syntax minted by the TimeGate and TimeMap, not a query knob: pick a datetime via Accept-Datetime or from the TimeMap and follow the links. Memento responses carry Memento-Datetime and Link headers.

The TimeMap at /wms/timemap?layer=…&s=…&bbox=… lists the memento URIs for the bbox in application/link-format; /wms/timemap.json adds per-date cloud cover and drives the map page's time slider. Default window is the last 365 days; pass time={interval} for other windows. For Sentinel Hub WMS layers, &maxcc=20 limits the maximum cloud cover in percent.