Approximately half the population of Germany lives in the 30 major urban German agglomerations, such as Berlin, Hamburg, Munich (München), and Cologne (Köln) but also in smaller cities including Münster, Freiburg, Leipzig, and Dresden. These urban regions (Stadtregionen) are also major analytical units of the Federal institute for Research on Building, Urban Affairs and Spatial Development (BBSR) within the Federal Office for Building and Regional Planning that advises the Federal Government in the fields of spatial planning, urban development, housing and building. Therefore, these regions that cover approximately 32 per cent of the built-up area used for settlement or transport infrastructure are of particular interest in understanding urban dynamics in Germany in a regional and national context (Baumgart et al, 2016).

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The maps presented here are part of an analysis made using advanced methods of geovisualisation to aid a better understanding of recent trends in urban development. The maps are using two different approaches to cartogram techniques that focus on showing the population changes that occurred in these agglomerations. Cartograms are an increasingly used alternative to conventional maps. Recent advances have made these maps more versatile and suitable for advanced analytical purposes Tobler (2004). This work utilises the diffusion-based method for producing density-equalising maps by Gastner & Newman (2004) and further advances in their approach developed by Hennig (2013).
The main map is a gridded cartogram in which equally-sized grid cells are resized according to number of people living there. This transformation includes the entire area of Germany where the most densely populated regions are increased in size proportional to their populations and more sparsely populated rural areas are much smaller than they appear on a land area map. This allows additional spatial information such as socio-demographic data to be shown in their relation to population, such as the colours in this map are visualising the relative annual population changes that occurred in the major urban agglomerations between 2008 and 2013.
The two complementing maps are density-equalising cartograms in which only the major urban agglomerations are transformed while the surrounding administrative regions are shown for orientation only. These cartograms are depicting growth and decline which they show in two separate maps that highlight the quantitative extent of these changes. Each urban is present in only one of the two cartograms, indicating that it was either subject to an increase or a loss of population this time period. By using such novel visualisations dynamic changes, such as shifting populations, can be analysed in their spatial as well as their human context.
Examination of the average annual change in the populations of the selected urban agglomerations highlights the regional differences in these trends. Contrary to the national population decline of the past 30 years, which is predicted to slow down or reverse in future, 26 out of the 30 major agglomerations show population growth between 2008 and 2013. In 25 of these areas population growth in the city centre is even higher than in its respective suburban area. This can be seen as evidence of a very recent trend of re-urbanisation in these places.
One particularly notable trend is the dynamics in smaller cities such as Freiburg and Münster, as well as Dresden and Leipzig in east Germany. In addition to high rates of re-urbanisation, the suburban areas often have stagnating or even declining populations.
The Ruhr area agglomerations are distinctively different from the other areas described in the overall summary of trends. The stagnating populations in the centres of Dortmund and Essen are complemented by considerably declining populations in their surrounding areas.
The smaller pair of cartograms helps to understand that population decline in the settlements in the Ruhr area that is larger than in all other urban agglomerations put together. Growth, in contrast, is spatially spread much more evenly.
Amongst the influencing factors or growth and decline are developments in social structures, employment as well as changes in land development in these regions. How these factors are interconnected and influence each other is part of further research towards a long-term geomonitoring of these regions in order to better understand these new forms of urbanisation in Germany (Baumgart et al, 2016).

References:
Baumgart C, Kaup S, Osterhage F, et al (2016) Monitoring StadtRegionen. In: Othengrafen F, Schmidt-Lauber B, Hannemann C., et al (eds) Jahrbuch StadtRegion 2015/16. Leverkusen-Opladen: Budrich, pp.219–264. DOI: 10.3224/jbsr.v9i1.12
Gastner M and Newman M (2004) Diffusion-based method for producing density equalizing maps. Proc. Natl. Acad. Sci. USA 101: 7499–7504. DOI: doi.org/10.1073/pnas.0400280101
Hennig BD (2013) Rediscovering the world: Map transformations of human and physical space. Heidelberg: Springer. DOI: 10.1007/978-3-642-34848-8
Tobler W (2004) Thirty-five years of computer cartograms. Annals of the Association of
American Geographers 94 (1): pp.58–73. DOI: 10.1111/j.1467-8306.2004.09401004.x
Additional data source:
Statistische Ämter des Bundes und der Länder (2015) Ergebnisse des Zensus 2011, Bevölkerung im 100 Meter-Gitter (accessed 1 July 2018).

Bibliographic details for the original publication that this blog entry is based on:

• Hennig, B.D. (2018): The growth and decline of urban agglomerations in Germany. Environment and Planning A: Economy and Space. DOI:10.1177/2F0308518X18798835

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