Celebrating census

Maps using data from population censuses have been published in The Journal of Maps since its inception and this source of data often acts as a fundamental input to research undertaken by social scientists as well as researchers from other disciplinary areas. Mapping of population data is no longer the preserve of a limited range of disciplines but occurs across the spectrum of social as well as the natural sciences where human-environmental interaction is at the forefront of our concern. For this edition, we invited contributions focused on the evolving character and cartographic opportunities offered by traditional census statistics and the impact of transitioning from these into a new era of assembling ‘big data’ from diverse data sources.

Seeking an international dimension to the contributions in this special issue, 2021 also marked two notable events in the history of British census taking: the 100-year anniversary of the first national enumeration of the population held under the auspices of the 1920 Census Act and what was expected to be last British census conducted in this manner. We also sought to showcase and exemplify cartographic representation of population data and to explore opportunities for visualising demographic information amalgamated from administrative and bespoke surveys of population.

The established history and regularity of holding a population census in many countries affords opportunities to investigate and visualise change in their populations over time. Two papers illustrate the challenges and rewards of such endeavour: Aucott and Southall (2022) took on this challenge for censuses spanning 170 years, whereas O’Driscoll et al. (2022) focus on a shorter 30 time period, although in a country where quinquennial censuses resulted in seven enumerations. Their map addressed the challenge of visualising population growth, stasis or shrinkage for small administrative units over seven time periods charting consistency or variation over the entire period. Although O’Driscoll et al. (2022) encountered a change in the boundaries of their spatial units, Aucott and Southall’s (2022) map involved re-districting historical administrative geographies spanning nine decennial censuses (there was no census in 1941) to conform to the 380 districts existing in 2011. Additionally, they faced re-classification of historical occupation and industry coding schemes to comply with the 20 ‘Sections’ of the 2007 Standard Industrial Classification.

The geographical ubiquity of censuses in many countries as a means of collecting population statistics suggests the opportunity for a degree of comparability and international comparison. The United Nations has assumed the role of harnessing and disseminating global population statistics and in 1958, to help with fulfilling this function as well as assisting national statistical offices and census officials, it issued guidance on the principles and recommendations in respect of conducting population and housing censuses. Garnica-Monroy and Hernández-Reyes (2022) remind us that discussion and visualisation of census statistics is not the same across all countries as Mexico is one with an Extended Questionnaire schedule addressed to a Census Sample rather than the whole population.

The range of topics in a census and therefore also topical coverage of census statistics tends to be more limited than sample surveys carried out by national statistical offices. Lengyel et al. (2022) demonstrate the key strength of these characteristics is the opportunity to undertake multivariate analyses in conjunction with another data source to generate socioeconomic profiles. The ability to combine data from censuses and other sources itself has paved the way for a future where ‘census like’ information is assembled from a variety of sources.

Censuses are generally regarded as presenting a cross-section or snapshot view of a population at a certain time whose currency decays through the following years until the next enumeration occurs. Lomax (2022) focuses on the census question asking about people’s address one year before the census date demonstrating how it is possible to explore changes in the rates and spatial patterns of internal migration over the four decennial censuses from 1981 to 2011. Recent developments in ‘big data’ and our shift into the era of ‘data science’ seem likely to mean that the days of traditional censuses may be numbered. This transition is reflected in the paper by Mileu et al. (2022), which explores population mapping using open source address data to address the basic question, where is the population? Using a bottom-up approach they produce gridded maps to answer this question in Portugal at a spatial resolution and frequency that would be unrealistic with the traditional decennial census. Others might contend there remains merit in a ‘small data’ approach, where specific questions are asked to get specific answers, rather than amalgamating data originally collected for a different purpose. Some countries, such as the USA, also have a constitutional or statutory requirement guaranteeing conduct of a traditional census, although repeal of such legalistic underpinning could occur.

We would like to express our gratitude to the 18 reviewers who have generously given their time to review the papers submitted to this special issue. We would also like to thank the authors for responding so positively to the invitation for contributions: the outcome is a set of inspiring and stimulating papers demonstrating the variety and complexity of issues involved with visualising census statistics and giving a foretaste of the future with the mapping of newer types of population data. Finally, we would like to acknowledge the unparalleled support and guidance of Mike Smith and his team, which has made the whole process of steering this special issue from an idea to a reality such a ‘pain free’ one.