Agglomeration economies are a persistent subject of debate among economists and urban planners. Their definition turns on whether or not larger cities and regions are more efficient and more productive than smaller ones. We complement existing discussion on agglomeration economies and the urban wage premium here by providing a sensitivity analysis of estimated coefficients to different delineations of urban agglomeration as well as to different definitions of the economic measure that summarises the urban premium. This quantity can consist of total wages measured at the place of work, or of income registered at the place of residence. The chosen option influences the scaling behaviour of city size as well as the spatial distribution of the phenomenon at the city level. Spatial discrepancies between the distribution of jobs and the distribution of households at different economic levels makes city definitions crucial to the estimation of economic relations which vary with city size. We argue this point by regressing measures of income and wage over about five thousands different definitions of cities in France, based on our algorithmic aggregation of administrative spatial units at regular cutoffs which reflect density, population thresholds and commuting flows. We also go beyond aggregated observations of wages and income by searching for evidence of larger inequalities and economic segregation in the largest cities. This paper therefore considers the spatial and economic complexity of cities with respect to discussion about how we measure agglomeration economies. It provides a basis for reflection on alternative ways to model the processes which lead to observed variations, and this can provide insights for more comprehensive regional planning.

Scaling laws are simple, easily usable and proven relevant models used in geography for validating various urban theories. These non-linear relationships may reveal physical constraints on the structure and evolution of complex systems, and underline the relationship between urban functions, size of cities and innovation cycles. In this contribution, we examine to what extent scaling laws are transferable towards urban theories and in which specific fields of urban geography these models may be relevant. We thus focus on the accuracy of scaling laws when exploring structures and processes of systems of cities, the diffusion of innovation, metropolization and intra-urban dynamics. We therefore use several examples taken in different regions of the world, embedded in various historical, political and economic contexts. However, in some cases, care must be taken not to over-interpret the results obtained from scaling laws and not to give scaling laws more explanatory power than they can describe. We illustrate this point by providing recommendations relying for instance on the sensitivity of measurements to the delineation of each object of the system under study and to the definition of the system itself. These recommendations can help to get robust results in order to understand the generic evolutionary mechanisms in urban systems.

Both theoretical and empirical studies have shown the ability of scaling laws to reveal processes of emergence in urban systems. Nevertheless, a controversy about the robustness of results obtained with these models on empirical cases remains, regarding for instance the definition of the ‘city’ considered or the way the estimations are performed. Another source of bias is highlighted in this contribution, with respect to the non-ubiquitous character of some urban attributes (i.e. their partial absence from several cities of the system). The problem with the zero count for cities where these attributes are absent is that the technical necessities of usual estimation procedures make the analysis ignore them altogether even when they represent some valid information. This could seriously impact the results. A precise exploration of the effects of this arbitrary filtering is conducted here, and several solutions are proposed to overcome this limitation. In a case study about foreign investment towards French cities, we show that some erroneous conclusions about a hierarchical diffusion could be drawn when adopting the classical ordinary least squares approach. The framework we suggest specifies how it is possible to avoid misinterpretations deriving from the exclusion of zero values by using methods of analysis which deal with zero values specifically. The conclusion of a diffusion of foreign investment in the French urban system is then rejected.

Despite the fact that freight transport has a huge impact on the economy and the environment, datasets have always been scarce or restricted to very small a-spatial samples. We here aim at diverting spatial data collected in Belgium for tolling trucks proportionally of their use of the road network, and at further extracting geographical structures and dynamics out of this massive dataset. The paper first relates to the numerous problems encountered when using and transforming big data generated by On Board Units GNSS (cleaning, transforming and preprocessing), second it maps and comments movements (traffic) and stops of trucks within the entire country, and finally partitions the country into mathematical communities of places that most interact. Analyses are performed for the complete sample, but also for sub-categories based on the country of registration underlining the spatial specificities of freight transit in Belgium. This exploratory spatial data analysis enables to reveal multi-level spatial structures associated to urban hierarchies, transport infrastructure but also firm locations or political organizations, tickling the complexity and interconnectivity of any measure taken for a more sustainable future.

Change detection approaches based on historical maps are frequently used in fluvial geomorphology to reconstruct long‐term river trajectories and evaluate the level of functional degradation. On this basis, achievable rehabilitation goals may also be addressed. However, most of these studies explore the changes of land cover over time only through changes in the landscape composition, which is nevertheless not sufficient to assess accurately the river responses to natural and/or man‐made disturbances. In this study, we present that transition matrices and new metrics derived from this approach can be used to evaluate the land cover and ecotone area changes at multispatial scales on a 6 km long reach of the Upper Rhine. This study was based on the historical maps of 1828, 1838 and 1872 and using Open Street Map (OSM) for 2021. Our approach was targeting to assess (i) the composition and configuration of a fluvial landscape over time from pixel to landscape scale, (ii) the accurate location of land cover changes, their nature and their intensities, and (iii) the location, nature and diversity of the ecotone areas and their spatial complexities over time. The results showed that (i) the absence of changes in landscape composition over time cannot be interpreted as stability in the fluvial landscape in all cases, (ii) transition matrices are robust tools to face interpretation biases caused by conventional approaches based on landscape composition, because they allow us to trace the changes of each element of the transformed landscape elements. From this study, we indicate that the Rhine regulation induced a habitat and ecotone homogenization following the river correction works, which was exacerbated by the Rhine by‐passing, mainly due to the degradation of lateral connectivity between the main channel and the floodplain and global loss of the hydrosystem functionality.

À l’échelle mondiale, les firmes transnationales sont à l’origine d’inégalités d’intégration substantielles. Il est bien connu qu’elles dirigent notamment leurs investissements avant tout depuis et à destination des pays du Nord. Peu observées à l’échelle des systèmes de villes, leurs stratégies de localisation placent pourtant les villes dans des positions très diverses : certaines se situent en tête de leurs réseaux, certaines se trouvent très intégrées en accueillant de nombreux investissements, d’autres encore en sont quasiment exclues. Nous observons l’inégale intégration des territoires aux réseaux des firmes étrangères en France, à une échelle plus fine que celle permise par la seule considération des statistiques conventionnelles, et ceci dans une perspective dynamique. Alors que les métropoles sont concernées en tout premier lieu par une mondialisation incluante, les villes plus petites sont engagées dans des trajectoires d’intégration très diverses : marginalité, rattrapage, renforcement et déclin. Ceci a pu être révélé par la décomposition des réseaux de filiation des firmes transnationales via une base inédite des établissements sous contrôle étranger dans les aires urbaines françaises et leur comparaison à un recensement des établissements nouvellement créés depuis 2003.

No abstract

Revue trimestrielle sur l'image géographique et les formes du territoire