International, relevant to the Netherlands

Wikidata

Wikidata is the free knowledge base behind Wikipedia: millions of items (people, places, buildings, organisations, artworks) with properties and sources, and above all with the IDs other registers use. For the Netherlands these include national monument numbers (P359), CBS municipality codes (P382) and KvK company IDs (P3220). This lets you join datasets that have no common key of their own. Everything is CC0. Note: robots.txt disallows bots on the SPARQL service and the APIs, so the Open Data Index does not query Wikidata itself.

Heritage and culture Government PopulationOpenAPIDownloadSearch serviceWorld · item (person, place, building, organisation …)

Reachable · checked 17:23

Museums in the Netherlands by theme (CBS count): history is the largest part, 65% in 2024

Breakdown in 2024: history 65%, art 21%, industry and technology 7.6%, natural history 4.7%, ethnology 1.6%. Total: 621 museums.

Source: CBS, tabel 83533NED (Musea; collectie, bezoeken, tarieven, tentoonstellingen, werkgelegenheid) · opgehaald 25 oktober 2026Open the table Single block

What can you do with it?4 ideas

Getting started

From monument number to photo and Wikipedia

Look up a national monument by its number (P359) and you often find a photo on Wikimedia Commons, the Wikipedia articles and the architect.

Getting started

Museums on the map

Ask for all items that are a museum (Q33506) in the Netherlands (Q55), with coordinates and municipality. Put them next to the CBS museum statistics: what does CBS count that Wikidata does not?

Advanced

Finding abolished municipalities

P382 also gives CBS codes of abolished municipalities. You can use them to map old figures to today's boundaries, but check the end date; it is sometimes missing.

Advanced

Politicians and their careers

Items of MPs often have party, positions with start and end dates and place of birth. Link them to the House of Representatives data by name and check for duplicate names.

How to process it4 steps

Look at an item
Each item page shows the properties with sources. Q55 is the Netherlands, Q33506 is museum; P359 is the national monument number.
```
https://www.wikidata.org/wiki/Property:P359
```
Try a query in the browser
The Query Service has an editor with examples and map and chart views. A query may run for 60 seconds; per user agent and IP you get 60 seconds of processing time per minute, 30 failed queries per minute and 5 in parallel.
```
https://query.wikidata.org/
```
Follow the user-agent policy
If you query from a program anyway, send a user agent with a name and contact. Without a good user agent you can be blocked; on 429 wait for Retry-After. Read robots.txt and the terms yourself.
```
https://meta.wikimedia.org/wiki/User-Agent_policy
```
Everything in one file
A full dump appears every week. latest-all.json.gz was 156 GB on 13 October 2026; each line is one item as JSON, so you can read it line by line.
```
https://dumps.wikimedia.org/wikidatawiki/entities/
```

Interesting combinations

rijksmonumentnummer (P359)

Which monuments have no photo yet?

Compare monument numbers from the RCE register with the items in Wikidata and find the numbers without an image.

Combine with Register of national monuments

CBS-gemeentecode (P382)

Municipal figures with mayor and photo

Join CBS figures per municipality to the Wikidata item via the municipality code and add the mayor, coat of arms and Wikipedia link.

Combine with CBS StatLine

Similar sources

Register of national monuments
The official monument register of the RCE, with legal status and description. Wikidata adds photos, architects and Wikipedia links, but is not official.
OpenStreetMap
OpenStreetMap has the geometry (buildings, roads) and often points to the item with a wikidata tag. Wikidata has the facts and IDs, OSM the map.
Europeana
Europeana gathers collections from museums and archives, with images and metadata per object. Needs a key.

What to watch out for

robots.txt disallows bots
query.wikidata.org disallows /sparql and www.wikidata.org disallows /w/, /api/ and /wiki/Special: for all user agents. We do not query Wikidata ourselves; the chart here comes from CBS.
Anyone can edit
Wikidata is maintained by volunteers. Check the source of each fact, and use it for linking and exploring, not as an official register.
Completeness varies
Whether something is in Wikidata says nothing about whether it exists. Counts (so many museums, so many monuments) are counts of Wikidata, not of reality.
Queries time out
Broad queries (all people, all buildings) do not finish within 60 seconds. Narrow down to the Netherlands or a class, or use the dump.

APISPARQL 1.1 (Wikidata Query Service) · read 16 Oct 2026

StandardSPARQL 1.1 (Wikidata Query Service)docs

Access no key

No key, but a User-Agent with a name and contact (otherwise the service may block you). from the description

Size120,000,000

items ('over 120 million Items' according to Wikidata:Data access, Oct 2026) from the description

Formats

sparql-results+xmlsparql-results+jsoncsvtsvjsonrdfturtlen-triplesjson-ld

Base URL

https://query.wikidata.org/sparql

Endpoints 7

GET/sparql?query=…SPARQL query in the URL; XML by default, JSON with Accept or format=json. Main graph only: scholarly articles are on query-scholarly.wikidata.org since the graph split.
POST/sparqlThe same query as form field query= (for long queries).
GEThttps://www.wikidata.org/wiki/Special:EntityData/{Q-id}.jsonLinked Data Interface: one complete item as JSON (also .ttl, .nt, .rdf, .jsonld); http://www.wikidata.org/entity/Q55 redirects here.
GEThttps://www.wikidata.org/w/rest.php/wikibase/v1/entities/items/{Q-id}Wikibase REST API (OpenAPI): read and edit items and statements.
GEThttps://www.wikidata.org/w/api.php?action=wbsearchentities|wbgetentitiesMediaWiki Action API: search by label, fetch up to 50 items per request, edit.
GEThttps://dumps.wikimedia.org/wikidatawiki/entities/Full dumps (JSON, one item per line; also RDF), every week.
GEThttps://stream.wikimedia.org/Recent Changes stream (server-sent events) of all Wikimedia wikis; filter Wikidata yourself.

Filtering from the description

SPARQL 1.1 with the Wikidata prefixes and the label service. Example: ?m wdt:P31/wdt:P279* wd:Q33506 ; wdt:P17 wd:Q55 (all museums in the Netherlands).

SELECTFILTEROPTIONALpad/pad*GROUP BYSERVICE wikibase:labelSERVICE wikibase:around

Parameters 7

`query`	The SPARQL query (GET or POST).	from the description
`format`	json or xml; or the Accept header: application/sparql-results+json, text/csv, text/tab-separated-values.	from the description
`wd: / wdt: / p: / ps: / pq:`	Items (wd:Q55), direct properties (wdt:P31), full statements with qualifiers (p:, ps:, pq:). Predefined in WDQS.	from the description
`SERVICE wikibase:label`	Labels automatically: ?xLabel for ?x, with bd:serviceParam wikibase:language "nl,en".	from the description
`P31 / P17 / P131 / P625 / P18`	instance of, country, located in the administrative territorial entity, coordinate location, image.	tested
`P359 / P382 / P3220`	Rijksmonument ID, CBS municipality code, KvK company ID: the join keys to Dutch registers.	tested
`Q55 / Q2039348 / Q33506`	Netherlands, municipality of the Netherlands, museum.	tested

SPARQL result (W3C standard) 3

Name	Type	Meaning
`head.vars`	lijst	Namen van de variabelen in het resultaat
`results.bindings[].<var>.value`	tekst	Waarde per variabele (URI, tekst of getal)
`results.bindings[].<var>.type / datatype / xml:lang`	tekst	Soort waarde (uri, literal), datatype en taal

Limits and pitfalls

Every query stops after 60 seconds. Per client (User-Agent + IP) 60 seconds of processing time per minute, 30 failing queries per minute, 5 in parallel per IP; above that HTTP 429 with Retry-After. from the description
Action API: up to 50 items per request; use maxlag and request gzip (Accept-Encoding). from the description
The robots.txt of query.wikidata.org disallows /sparql and /bigdata; that of www.wikidata.org disallows /w/ (so rest.php and api.php), /api/ and /wiki/Special: (so Special:EntityData). The Open Data Index therefore does not call these endpoints; everything here comes from the documentation. tested
robots.txt is aimed at crawlers; Wikidata itself invites programs to use the Query Service, with a good User-Agent. For large volumes: the weekly dump. from the description
Since the graph split, scholarly articles are no longer in the main graph but on query-scholarly.wikidata.org. from the description
Broad queries (all people, all buildings) do not finish within 60 seconds. Narrow to the Netherlands or a class, or use the dump. experience
Wikidata also lists a GraphQL API, a vector database (wd-vectordb.wmcloud.org) and an MCP server (wd-mcp.wmcloud.org/mcp/). from the description

Try it

No example call: the robots.txt of query.wikidata.org disallows /sparql and that of www.wikidata.org disallows /w/, /api/ and Special:EntityData. Try the query yourself in the editor at query.wikidata.org.

Read from Wikidata: all ways to access data (search, Linked Data, WDQS, REST, Action API, GraphQL, dumps, MCP) · Query Service manual: formats, limits, label service, namespaces · Wikimedia User-Agent policy. Labels: from the description stated in what the api itself publishes. tested from our own small call. platform applies to every api on this platform, per its documentation. experience learned while building open data index.

More from Wikidata in our index

1 datasets in NDE Datasetregister. These changed most recently.

All about Wikidata