Open data platform for municipalities

An open data platform has two tasks. It is the place where residents, researchers and businesses find the municipality's datasets, with a description, licence, currency and download links or APIs. And it is the source from which national and European portals take over those descriptions, so that the municipality maintains each dataset in only one place.

That second task is often underestimated. data.overheid.nl is the national data portal, and the European Data Portal takes all Dutch datasets from there. According to data.overheid.nl, with automatic delivery datasets are registered only once and maintained in one place by the source owner. A platform of your own that connects well therefore makes sure your datasets are also findable at European level without double work.

A platform is more than a catalogue, though. Behind every dataset sits a file or service that must be stored somewhere and kept current. For geodata that is often a map service or an OGC API; for tables a CSV file or an API on a database. Where that data sits and how it is updated is described on the page about data platforms. This page is about the catalogue and the connection to national infrastructure. If you are on the other side and want to reuse national datasets, start with the guide to Dutch open data.

If you still have to decide whether you need a platform of your own or whether registering with data.overheid.nl is enough, see the guide publishing open data as a municipality (in Dutch).

data.overheid.nl describes ways for a government organisation to get datasets onto the portal. Which route fits depends on the number of datasets and on whether you already have a catalogue of your own.

With the API route, according to data.overheid.nl, you get access to a test environment and an agreement with the main arrangements. What does not happen is also important. With this kind of delivery data.overheid.nl stores no data, only the link to it. The municipality itself therefore takes care of storing the files and keeping them reachable.

DCAT-AP-NL is the Dutch application profile for exchanging descriptions of datasets and data services between catalogues. Version 3.0 is a Geonovum standard; the adopted version is dated 26 May 2025. The profile builds on the European DCAT-AP 3.0 and incorporates the requirements for High Value Datasets, so that whoever meets the Dutch profile can also meet the European requirements for open data and High Value Datasets.

Forum Standaardisatie announced on 5 October 2026:

Het Overheidsbrede Beleidsoverleg Digitale Overheid (OBDO) heeft dinsdag 29 september 2026 ingestemd met het voorstel van het Forum Standaardisatie om op verzoek van de indiener de status ‘Pas toe of leg uit’ toe te kennen aan versie 3.0 van de standaard DCAT-AP-NL.

Source: Forum Standaardisatie, DCAT-AP-NL. In other words, the government-wide policy body for digital government gave DCAT-AP-NL 3.0 "comply or explain" status, which applies from 1 January 2027. A platform you set up now should therefore be ready for that version.

At the same time data.overheid.nl reports that the portal currently still uses its own profile DCAT-AP-DONL 1.1, which will be replaced in the foreseeable future by a DCAT 3 profile. For the technical connection data.overheid.nl requires that all mandatory fields are filled, only permitted values are used and every dataset has a unique, persistent identifier.

In practice that means a platform that records the metadata once internally and can deliver it per consumer in the requested profile. If data.overheid.nl switches, only the translation changes, not the input of your staff.

CKAN is an open source data management system for data portals and data hubs. The software is under the GNU Affero General Public License version 3. Among other things, that licence requires that whoever offers a modified version as a network service makes the source code of those modifications available. For a municipality that is rarely an objection, but it belongs in the trade-off.

For the Dutch context the extension ckanext-dcat matters most. According to its documentation it offers DCAT endpoints that deliver the catalogue in several RDF formats, a harvester that can read RDF from other catalogues, and a mapping between CKAN and DCAT that supports DCAT-AP 1.1, 2.1 and 3. The profiles can be adapted, and that is where the work for DCAT-AP-NL lies. The fact that data.overheid.nl itself offers the CKAN API for delivery makes the connection technically straightforward.

CKAN is not always the best choice. If you have a handful of datasets, registering manually with data.overheid.nl is simpler than running a platform of your own. If almost all your open data is geodata in the Nationaal Georegister, delivery already runs through that register. And if you mainly want dashboards or stories alongside data, a different type of product fits better. The trade-off between CKAN and alternatives is worked out in CKAN or an alternative (in Dutch).

Every dataset needs a licence that says how it may be reused. data.overheid.nl lists public domain, CC-0, CC-BY and CC-BY-SA as open licences, and points out that CC-0 makes clear to reusers that the data can be used without restriction. Geo Gedeeld has standard terms of use and can lead to restrictions; a dataset with such a restricted licence does not count there as open data. The choice is a decision for the municipality, not for the builder. The platform does make the chosen licence visible and machine-readable per dataset.

Before data becomes open, according to data.overheid.nl a legal check must take place: does opening it conflict with a rule of law? That includes the GDPR (AVG in Dutch) if a dataset can contain personal data, including indirectly, for example through combinations of location and date.

data.overheid.nl names the Data Governance Act, the Wet hergebruik overheidsinformatie (Who, the Dutch law on reuse of public sector information) and the Wet open overheid (Woo, the Dutch open government act) as the main laws around open government and transparency. Which obligations follow from them for a specific dataset is a legal question that lies with your municipality. The platform supports the outcome, for example with a field for the legal basis, a publication status that becomes public only after approval and a log of changes.

1. Inventory. Which datasets exist, who owns them, where are the files and which are already in the Nationaal Georegister? The result is a list with, per dataset, the status and the desired licence.
2. Demo instance. A CKAN environment with a few of your public datasets, so that editors can try out data entry and you see the public side.
3. Metadata profile. We align the fields with DCAT-AP-NL 3.0 and with the profile that data.overheid.nl expects at that time, including persistent identifiers.
4. Connection to data.overheid.nl. Testing in the test environment of data.overheid.nl, then the production connection through API or harvest.
5. Populating and training. Existing descriptions are transferred where possible, and editors learn to add and update datasets.
6. Go-live and handover. The platform goes live on your domain, with a management manual, infrastructure code and an agreement on updates.

In the platform, geodata gets a reference to the associated map service or OGC API, so that visitors can also click through to a map. If your municipality also shows that data in a viewer of its own, that connects to a GIS viewer for municipalities.

Part of the work can only be done by the municipality. That starts with the organisational conditions of data.overheid.nl.

• An approved data owner account on data.overheid.nl. Only (government) organisations are approved as data owners, and you need permission to register datasets on behalf of the municipality.
• A fixed email address for questions and data requests about the datasets.
• An owner per dataset who maintains the content and decides on openness and licence.
• The legal check per dataset, with a decision on personal data.
• Storage of the data itself, because data.overheid.nl keeps only the link. That can be in the same platform, on a server of your own or at a hosting partner.
• Editorial time to keep descriptions up to date. A catalogue with outdated datasets damages trust more than a small, current catalogue.

TechinFlow can think along on every point and carry out the technical side, but the decisions and the responsibility lie with the municipality. Start small, therefore, with the datasets whose owner and licence are already settled.

CKAN regularly releases new versions, and extensions such as ckanext-dcat move along with new DCAT versions. A management agreement records who tests and carries out updates, and how quickly security updates are applied. The platform runs in containers and the environment is held as code in a repository of the municipality, so that rebuilding at another hosting partner remains possible. Hosting in the EU is our starting point; the choice and the agreements on it are described under cloud and data infrastructure.

Exiting an open data platform is relatively simple if it has been well prepared. Through the DCAT endpoint the entire catalogue can be requested in an open format, and other catalogues can read it. Our own adaptations to CKAN are delivered as a separate extension in your repository, not as a change to the core, so that a successor can simply update CKAN.

TechinFlow B.V. develops custom software, GIS and map applications and data platforms, with a focus on government bodies and organisations. It is a new company in Haarlem, founded by Tekin Uslu. By his own account, Tekin has worked on geo-information, data engineering and IT architecture since 2006. A conversation about your datasets starts through the contact page.