Podcast: OGC API Features and INE Census Sectioning: geospatial interoperability in practice

This episode focuses on interoperability in the field of geospatial data, open standards and collaboration between public bodies, based on a recent novelty of the National Institute of Statistics: the publication of access to the Census Sectioning through OGC's API Features standard. 

This initiative is part of a broader context of modernization of geospatial services and a commitment to open standards that facilitate the reuse of information, integration between systems and joint work between institutions. 

 Geographical data and statistical data are increasingly intertwined, for example in territorial analysis, public planning or research. And in this context, having interoperable services is key to moving towards a true shared ecosystem. 

To address this issue, two experts in the field have been interviewed:

• Paloma Abad Power, deputy deputy director of the National Center for Geographic Information (CNIG), attached to the National Geographic Institute (IGN).
• Nazaret García Seijas, advisory member of the Support Unit of the General Directorate of Population Statistics of the National Institute of Statistics (INE).

Listen to the full podcast (only available in Spanish)

Summary/Interview Transcript

1. Many people in the statistical or geographical field know about the Census Section, but perhaps not everyone is clear about what exactly it represents.  Could you explain to us what the Census Section is and why it is such an important product within the work of the INE?

Nazaret García: The Census Section is the geographical layer that represents the division of municipal land into districts and census sections, which constitute the basic territorial units on which most of the statistical operations of the INE are based. For example, population censuses, municipal registers or many other statistics with territorial disaggregation use precisely this structure to organise information. 

In practice, what the Sectionado does is to divide each municipality into one or more census sections, so that the entire municipal territory is covered by a mesh. 

In addition, the boundaries of each section are supported by elements recognizable on the ground. They can be streets, permanent constructions or natural accidents, and the premise is established that the same block is not divided into different sections. There is another important aspect and that is that the size of the sections is not arbitrary. The electoral legislation establishes a minimum and maximum range of voters per section. This means that the Census Section is a living product, which is reviewed and adjusted when demographic or territorial conditions change. From a technical point of view, the entire Sectioning is published inthe reference system ETRS89 (European Terrestrial Reference System 1989), huso 30, so that the information maintains a common spatial reference throughout the territory and can be combined with other geographical data without any problem.

2. From the perspective of the IGN and spatial data infrastructures, how is a product like the Census Section perceived within the geospatial ecosystem?

Paloma Abad: Within the geospatial ecosystem, the Census Section is perceived as a fundamental piece of territorial reference. Like the administrative units, in addition to being an official data, it is the frame of reference for the census or demographic analysis. Itis a high-value resource that must be provided, access must be allowed to users so that this data can be reused. That is why the INE strives to evolve and open new ways of accessing this data, as is the current case of API Features. 

Access to the data of the Census Section in an interoperable way was and is essential. Not only does it allow the user to locate and reuse this data from a given municipality, but it also allows them to integrate it with other data and establish automatic reuse flows. In addition, the Census Section is classified under the Inspire topic entitled "Statistical Units". 

3. How has the Census Section been traditionally accessed? What options did users who wanted to work with this data have until now?

Nazaret García: The INE has been publishing the Census Section for many years and offering different forms of access. The most traditional way has been the direct download of files in Shapefile format from the INE website, designed above all for use in GIS writing software(geographic information systems). In addition, we also publish various services, including:

• Web Map Services, mainly oriented to the visualization of cartography.
• Web Feature Service, which allows you to directly query and download vector entities by applying filters by attributes or by location. 

These services were already based on open standards, which allowed for a significant degree of interoperability and made it easier for data to be used in combination with information from other bodies. Importantly, these options are still available. The incorporation of the new service does not replace the previous ones, but rather expands the possibilities of access.

Paloma Abad: We may think that the easiest way to access data is to download it from a website. In other words, the user enters the INE website and downloads the data. But what if you are a company or a city council that is working with tools such as QGIS, ArcGIS or gvSIG? You need to automatically invoke data through services. In this way, when you connect to the services you have the data fully updated. That's why viewing, downloading, or location services exist. Localization data are those that provide the description of the data, that is, through metadata. As for downloading, there have always been the Web Feature Service or the ATOM. The Web Feature Service was mostly for queries and the ATOM for bulk downloads and currently the Feature API. All this was imposed by the INSPIRE Directive as early as 2007, so it was quite pioneering.

4. The INE has recently published access to the Census Section through OGC API Features. What exactly does this service consist of and what does it contribute with respect to other forms of access such as the WFS?

Nazaret Garcia: The OGC API Features service  is a modern way to access vector geospatial data through web services. It is part of a new generation of standards from  the Open Geospatial Consortium, which take an approach much more aligned with current web APIs, based on REST-like architectures. This allows access to resources through clear URLs and structures, much easier for the user. In addition, the service can return the information in formats that are more common in web environments and data analysis such as JSON, HTML, CSV or other formats, depending on the query. This makes the service easier to consume from web applications, development environments, or modern data analysis tools. Unlike the Web Feature Service, this service has a web interface that allows you to explore the data and perform queries directly from the browser. This makes it much easier to use, as a user can view information or download data without the need to previously use  geospatial software, something that in many cases does happen with Feature Service Web services. In general, the service allows you to navigate the available resources in a fairly intuitive way. For example, it is possible to query published data collections, access entities using clear URLs, and apply spatial filters, defining a coordinate-delimited query spatial extent.

5. So far we have talked a lot about technology, but interoperability also has a lot to do with collaboration between institutions. How does this translate into practice, in the case of the Census Sectioning?

Nazaret García: It means that the Census Section is not used only within the INE. It is a set of data that is integrated into applications, analytics and services of other agencies. For example, the Census Sectioning is available in the CartoCiudad viewer, where it can be viewed together with other sets of geographic information. This is possible because services based on common standards are used, and in reality, collaboration is bidirectional. The INE also uses geospatial services published by other bodies. In fact, on the OGC API Features service page  of the Census Section, the basemap used for the preview is the street map of the National Geographic Institute (IGN). It is a very simple example, but it reflects very well how interoperability allows the services of different organizations to be integrated in a natural and transparent way for the user.

Paloma Abad: Once an organization publishes its data through interoperable services or APIs, the reuse of data multiplies. Organizations and businesses can connect their applications with services. These services can be located through metadata. Entering the catalogues you search for "INE" or "census sections" and you find the URLs. In the case of the census tract, the Feature API is now available. If, for example, a municipality wants to do a survey, it can load the administrative units and census tracts using visualization services, and then it can also connect to the Feature API from gvSIG, ArcGIS, or QGIS and connect to the data. The latest Regulation on high-value sets, which also classifies statistical data, promotes their reuse.

6. More and more geospatial services based on modern APIs and standards are appearing, but for many users it can be difficult to know where to start. What would you recommend to someone who wants to get started with this type of service, such as the new OGC API Features of the Census Sectioning?

Nazaret García: To facilitate this start, the INE has prepared a guide that is published and available to any user who wants to consult it. In this guide we explain in a very practical way how to start working with the service. We show, for example, how to use it from the web interface of OGC API Features itself, which is one of the main novelties and advantages over more traditional services such as the Web Feature Service. This interface allows you to explore the collections, see query examples, and understand how the API works in a fairly intuitive way. In addition, we include some examples of how to integrate the service into common GIS tools such as QGIS or ArcGIS Pro in the guide, so that users can easily incorporate it into their workflows. And something that we also think is important is that we are open to  user feedback. The greater the use of the service, the more information we will have to continue improving it and adapting the needs of both other organizations and the user community in general.

Paloma Abad: In the case of geographic information, I differentiate three levels by users: 

• First, the non-expert user, the street user, can consult it. It already has applications where, although it does not perceive it, it uses visualization services or download services, such as, for example, when we consult the cadastral reference. In this case it is also possible with the census section.
• In the case of a technical user, they can develop an application where they load these services and have a direct connection with the databases of any organization, in this case the INE, and the data can always be used and there is always room for improvement. In addition, there can be feedback  of "Hey look at this service, I prefer it to be this way" and thus improve.
• And finally, the fully expert user motivated by interoperability can participate in OGC to develop standards and specifications, and thus adapt the data better so that it can be published in a way that is more appropriate to users.