1For nearly a century now, historians have used currency circulation as an indicator of human contacts in time and space. More broadly, the circulation of people and goods in Europe has been the focus of extensive theoretical work in the social sciences (Hudson, 2004). One of the main obstacles for researchers is the difficulty of collecting data on mobility at European level, hindering their attempts to outline a geography of international mobility on the continent. The data at our disposal is mainly based on information segmented by means of transport and by the intra-European travellers involved, with mobility surveys regularly carried out with students, businessmen, tourists and commuters.
2When the euro was brought into circulation in 2002, French geographers hypothesized that a spatio-temporal analysis of the distribution of coins minted by each country could serve as a relevant marker for individual mobility across Europe. Carried and used by Eurozone residents in their everyday transactions, the single currency lends physical form of contacts between European regions. Spatial structures of varying clarity emerge from the picture of individual social interactions constituted by the mingling of coins. Those structures should reflect the different capacities of territories and social groups to make contact with each other within Europe.
- 1 The surveys were carried out as part of the Euro Spatial Diffusion Observatory (ESDO) founded by Cl (...)
3Between March 2002 and December 2011, 16 studies were carried out at regular intervals in France1 (Grasland et al., 2002), with over 22,000 purses “surveyed” and 300,000 coins observed and inventoried according to their face value and country of issue (see Annexes: Table 1).
4The results of the initial surveys enabled researchers to measure the gradual increase in the mix of euro coins circulating in France according to their geographical origin. Several factors explaining variations in the presence of foreign coins on French territory were highlighted initially (Grasland and Guérin‑Pace, 2004). Mechanical effects (the number and value of the coins in a purse) were distinguished from temporal effects (the period of time since the euro was brought into circulation) and the commonplace effects of spatial interaction such as proximity to the border of a euro-zone country or the population size of neighbouring countries (Berroir et al., 2005). The impacts of the individual characteristics of the coin carriers—age, profession, socio-professional category, place of residence—on the presence of foreign coins are more difficult to identify, as low-mobility individuals can come into contact with numerous foreign coins simply by living near an airport. A comprehensive approach embracing both the spatial interaction and socio-territorial effects is still missing.
5In this article we propose to analyse the information provided by the “markers” of international mobility left by coins at a given time in a given place, the aim being to distinguish the commonplace from the specific in the circulation of coins. As such, we examine the circulation of euro coins as an indicator of territorialized social interactions. We start by overviewing the data compiled by the Euro Spatial Diffusion Observatory (ESDO) surveys. We then go on to discuss the uneven distribution of foreign euro coins in terms of face value and the varying capacities of individuals to come into contact with foreign coins in line with their socio-demographic characteristics. Lastly, we seek to identify the reasons behind the presence of foreign euro coins in France, which depends on the territories in question.
6Collecting information on this complex subject was a challenge for researchers from a range of fields interested in this major European event. Beyond its symbolic aspect, the arrival of the euro constituted a novelty for physicists, who finally had before them an experiment whose initial conditions they controlled, and for geographers and demographers, the focus of this paper. Obviously, the objectives differed considerably from one discipline to another. For physicists and for mathematicians, for instance, the main aim was to estimate the time it would take to achieve a perfect mix of the coins, namely a state of balance whereby in each country the share of coins with a given origin would be stable (Bergman et al., 2002; Stoyan, 2002). To that end, researchers used Markov models with parameters describing the size of the population and the distance between countries, without taking account of the internal geographical diversity of the countries and the resulting territorial effects. For the sake of simplicity, these studies were based on a set of information collected on Internet, with the creation of ad hoc websites on which Internet users were encouraged to regularly detail the content of their purses, i.e. the value and origin of the coins therein. Despite the biases inherent to this collection method, these data made it possible to calibrate the predictive models developed by physicists (Stoyan, 2002; Seitz et al., 2009; Seitz et al., 2012).
7For researchers in the field of social sciences, the aim was more to estimate—in absence of data—the circulation of people across Europe. When the euro was brought into circulation in January 2002, all the coins were theoretically located in the country in which they were minted. The issuing country of a euro coin thus represents the first link in a chain of movements and exchanges. The presence of a foreign euro coin in France then indicates that it has crossed one or more borders, depending on its geographical origin, transported in line with the movements of one or more individuals.
- 2 Zones d’études et d’aménagement du territoire (Research and National Development Zones, or ZEATs) a (...)
8Using the complex object of currency to reveal the spatial mobility of Europeans on French territory hinged on the availability of representative data at the most exact territorial level possible. The protocol used in each of the surveys carried out by ESDO ensured that the sample was representative at ZEAT2 level with a sample of around 2,000 people for each survey (see Annexes: ESDO survey methodology).
9The data collected by the 15 surveys between June 2002 and December 2011 enabled researchers to analyse nearly 300,000 coins in over 21,000 purses. Over the course of the decade, the share of foreign coins observed in France rose by a factor of six, from 6% in June 2002 to 34% in December 2011 (see Annexes: Table 1).
- 3 A Lévy flight, named after the French mathematician Paul Lévy, is a special class of randomwalk in (...)
10Over the last ten years, US physicists have analysed the circulation of one-dollar notes across the United States with a view to furthering understanding on the diffusion of other phenomena, such as epidemics (Brockmann and Hufnagel, 2007; Brockmann and Theis, 2008). They have notably succeeded in establishing a link between the regularity of the spatio-temporal reach of the movement of the notes and a mathematical law known as Lévy flights3.
11The introduction of the euro stirred considerable enthusiasm on the part of European researchers in a range of scientific fields. Some researchers have focused on the process in which foreign coins have spread and mixed in the euro zone (Le Texier and Caruso, 2016; Stoyan, 2002; Seitz et al., 2009; Seitz et al., 2012), while others have studied the relationships between the carriers, their territories and the circulation of the coins (Berroir et al., 2005; Nuno et al., 2005; Sohn, 2009).
12The aims and approaches of these studies vary considerably, but the same premise holds for each one: apart from its mercantile nature and political, and even symbolic, function, a common currency serves as a marker of individual mobility in European space.
13The data compiled in the ESDO surveys cannot be used to make direct deductions of the movements of people from the spatial diffusion of euro coins in France. But we can use those data to observe the resulting spatial markers in varying time steps. These markers are not collected at the moment of the movement in space, as with a GPS for example, and do not consist of a series of staging points completed by each coin. It is after the event, on the basis of a series of photographs of the spatial distribution of the coins at regular time intervals, that we can see the redundancy of the flow of coins diffused from one place of reference to a given location, and that we can postulate on the markers of mobility.
14These markers of the circulation of euro coins can be interpreted as the markers of the circulation of people, since the movement of the coins mainly results from the movement of individuals and a succession of transactions (Grasland and Guérin-Pace, 2004). Coins are transferred from one individual to another either directly or through a commercial pool. And while these pools fuel the random mixing of the coins, it is the individuals who are the main drivers of the process through their daily movements and purchases.
15These transactions are made as part of a chain. A coin may circulate within the same country for a certain period of time and then cross a border as part of a business trip to a large city and henceforth be exchanged only in the new country. But coins may also circulate as part of incessant to and from movements between two countries in the daily border crossings of the local population.
16While the national symbol minted on a coin informs on its country of issuing, it tells us nothing about the precise location where it was brought into circulation, the paths it has taken, the miles covered or the number of intermediary carriers through to the observation point. As such, we cannot know precisely how many times it has entered or left a country; we can only estimate the output of the movements through the presence of coins of different origins in a given territory.
- 4 Resident here means any person having lived temporarily or permanently in a euro-zone country durin (...)
17Just as the transmission of family names (Darlu and Ruffié, 1992) and specific genes (Cavalli-Sferza and Edwards, 1967) from one world region to another sheds light on migratory movements, the circulation of euro coins reveals contacts between the residents4 of euro-zone countries. In the present study, we make the assumption that the higher the number of people circulating from one territory to another located abroad, the higher the number of coins carried between the two territories in question—and the more visible the markers of international mobility.
- 5 Multivariate binomial logistic regression models were implemented to estimate the probability of a (...)
18Our aim in this article will be to distinguish the factors explaining the high or low number of foreign coins in different parts of France and to determine the proportion of those coins by reconstructing a series of econometric models5. We will seek to go beyond the basic observation of the gravitational flows of coins into and out of the countries bordering France, which explain differences in the number of foreign coins in line with their origin and their diffusion after crossing the border (Grasland et al., 2012).
19The diffusion of foreign euro coins follows what Cliff (1981) refers to a “relocation diffusion” process. International mobility leads to a continuous rise in the number of foreign coins in a country, which itself leads to an increase in the number of international coins leaving the country. The long-term upshot of the process would be a “perfect mix” of coins regardless of origin, in other words a distribution of coins, proportionate to their respective weights in all the coins in circulation. The likeliness of a direct link between the issuing and the receiving countries becomes less and less certain as the mixing process goes on, erasing the markers of mobility. But contrary to the optimistic assumptions of physicists on the speed of the process, that mix is still far from being reached (Le Texier and Caruso, 2016), the process being slowed in particular by the regular minting of new coins by each country and new euro-zone members (Seitz et al., 2012).
20Numismatic historians have shown that the spatial diffusion of coins and notes differs according to their face value. This was for instance already the case in the Roman era, when bronze coins were used locally to buy bread, wheat, wood and pay craftspeople, whereas gold and silver coins, reserved for the elite, circulated in step with the movements of the representatives of power, major merchants and armies (Bursche, 2002).
21The same would appear to be true in the euro zone, whose inhabitants use different coins’ denominations for different purchases and adopt different payment strategies. Generally speaking, bronze coins bearing the lowest face values are used less frequently than the other coins, to the extent that some countries have already abandoned one- and two-cent coins (including Finland and the Netherlands) and rounded prices up to five cents. One reason for this is that users find the bronze coins hard to tell apart, so they tend not to use them at the moment of payment (Nuno et al., 2005; Le Texier, 2014). As was the case in the past, these differences impact the international circulation of coins according to their face value. The higher the value of the coin, the higher the probability of diffusion, thereby increasing the chance that the coin will be observed in a foreign country (see Annexes: Figure 1). Besides, the amount of foreign euro coins in France has been growing continuously since its introduction (see Annexes: Figure 1), introducing a further bias in the estimation of contacts on the basis of the diffusion of euro coins.
22These effects, which we qualify as mechanical, can be easily accounted for in modelling. We first sought to precisely measure their influence on the probability that a coin observed in a French money-bag at a given time was minted abroad or not (see Annexes: Table 2—model I). As expected, the likeliness of carrying a foreign coin increases with the period of survey (duration of the currency circulation) and the value of the coins.
- 6 But unlike contagion models, once the coin is transmitted to a new person, the transmission probabi (...)
23Coins are redistributed over time and across the euro zone in line with human mobility and through monetary transactions. The spatiotemporal propagation of foreign euro coins is largely driven by mobile individuals. That said, an individual with relatively low mobility but living in an internationalized territory may also be behind the diffusion of foreign coins. But we can make the assumption that, as in the case of epidemiological processes6, the probability of contact with euro coins issued abroad is related to the individual characteristics of the carrier.
24The probability for an individual to carry foreign coins in his/her purse depends on the structure of his/her social networks and mobility places. A person may also come into contact with foreign euro coins while travelling abroad or because he/she knows people and attends places connected to the rest of Europe. While it is impossible to distinguish between these two situations at individual level, we can observe whether some social groups tend to have more or less contacts with foreign coins than others.
25International mobility is socially differentiated, with some groups travelling very little towards limited and unvarying places. According to Castells (1996), the first level of the “space of global flows” is characterized by the spatial organization of dominant elites enjoying economic or decision-making power. International business travellers stand out from the rest of the working population through the regularity of their professional trips abroad, with up to several trips per month (Chevrier and Sauvage, 2006). In addition, the trip frequency and destinations of business travellers vary in line with their professional status, income and gender (Aguilera, 2008; Mallett, 2001). Individual and family characteristics also affect tourist travel, in terms of both constraints and preferences (Urry, 2012).
26Moreover, “transnational elites” have specific practices, attend certain types of places or city districts, and ultimately interact with only a few categories of the local population (Beaverstock, 2002). Consequently, the odds of the inhabitants of a given territory “picking up” a foreign euro coin will differ in line with their social category and daily habits.
27We introduced variables describing the socio-demographic characteristics of the respondents in the model accounting for mechanical effects in order to estimate their impact on the probability to possess foreign euro coins. The above-mentioned assumptions were confirmed by observing significant differences in the odd-ratios concerning gender, age and profession modalities (see Annexes: Table 2—model 2).
28We also observe that, all things being equal in terms of the other variables, men are more likely than women and young people more likely than older people to be in possession of a foreign coin. Socio-economic characteristics also play a role on the probability of having a foreign coin in one’s possession. Farmers are far less likely to come into contact with foreign euro coins than people in other socio-professional categories, apart from manual workers, with whom no significant difference was observed. Self-employed tradespeople and shopkeepers are the most likely to have foreign coins in their possession.
29These probabilities shift according to where the coin carrier lives. For example, a retired person living near the German border is more likely to come into contact with a foreign coin than a retiree in a small town in Brittany, even though the two individuals have the same daily consumption habits and similarly limited mobility. In the next part of this article we will seek to define the most internationalized territories from the viewpoint of the international circulation of coins.
30Our hypothesis here is that some euro-zone territories are more interconnected than others through the frequency and nature of individual mobility. On the basis of the findings of Grasland et al. (2005) and Le Texier (2014), we posit the existence of several temporal scales affecting international mobility in Europe that, combined with the distances travelled and the characteristics of the territories, can be used to make a connection between the circulation of euro coins and that of people.
31The daily to-ing and fro-ing across national borders results in a strong mix of coins over very short spatial distances, as part of a Brownian-type movement. As such, we assume that within these border areas, numerous coins cross and re-cross the border every day, owing to the cross-border movements of workers and consumers motivated by differences in salaries and prices.
- 7 The authors have previously tested different definitions of the distance effect, including linear, (...)
32More specifically, spatial diffusion models are based on the hypothesis that the probability of contact between individuals—and thus of the propagation of a phenomenon from one place to another—is stronger between places that are close together, as distance hinders the intensity of travel and, consequently, the frequency of contact (Tobler, 1970). Apart from the continuous effect of distance, the processes of spatial diffusion also show the presence of discontinuities, which result from a clear break in the intensity of the relations with the border country (Nijkamp et al., 1990). This neighbourhood effect, assuming it is limited to a restricted perimeter or one contiguous with a border, could be more simply resumed by a binary variable providing information on whether the town of residence of a respondent belongs to a border area or not (Ratzel, 1897)7.
33For its part, international mobility of business travelers occurs at a slower pace, leading to fewer border crossing for coins but carrying them across greater distances, thereby diminishing the probability of their returning to the country of issue. This would enhance the mixing process and results in peak numbers of foreign coins in specific places, namely large European cities.
34A number of studies, notably in the 1990s, have sought to characterize the degree of internationality of European cities (see for example Bonneville, 1994; Cattan, 1995; Pumain and Saint-Julien, 1996; and more recently, Cicille and Rozenblat, 2003). The attractiveness criteria used in the most recent studies are primarily based on cultural and academic influence, value-creating economic sectors such as finance, research, the presence of large business groups, and industry trade fairs and shows (Beaverstock et al., 2000). Another major criterion in this respect is the tourist appeal of large cities (Edwards et al., 2008). The human circulation resulting from these factors would suggest that these cities see a greater number of foreign coins.
35International tourist flows are highly seasonable (Baum and Hagen, 1999), with foreign coins arriving in a given territory in successive waves. This seasonal aspect being consistent from one year to the next (Kulendran and Wong, 2005; Croce and Wöber, 2009), we can measure the effect of tourism on the international movement of euro coins by distinguishing surveys carried out in the summer or around Christmas season from surveys administered in other periods.
- 8 It is worth noting that none of the touristic variables (provided online by the French national ins (...)
36Seasonal or annual mobility, then, plays a particular role in the process of transnational mobility, since it involves a considerable number of movements in very short periods of time and over varying distances. This type of mobility may not move a great number of coins when compared with the rest of the year as a whole, but it does constitute a significant mass of currency circulating towards tourist areas8.
- 9 Closeness here is considered as within 50 km of a border with a euro-zone country. This choice is t (...)
37To account for the geographic and seasonal effects previously described, we added a set of new explanatory variables to the model (i.e. in addition to the so-called mechanical and individual effects). We indicated the region in which the coin was observed (ZEAT), the population size of the municipality of residence of the respondent, its relative closeness to a national border9 and the seasonality of the survey (see Annexes: Table 2—model III).
38It can first be noted that the introduction of territorial and seasonal factors reduces the extent of mechanical and social effects, diminishing the significance of differences in professional categories and age while increasing differences in the face value of the coins or the survey year. It would appear that some of these effects interact with each other. As we assumed, it is after the summer and, to a lesser extent, after the end-of-year holidays that the number of foreign coins in France is at its highest. Adding the seasonal variable also helps us to more finely appraise temporal aspects.
39Secondly, some social and demographic inequalities regarding the probability of contact with foreign euro coins can be superimposed onto territorial inequalities, since a number of these effects become harder to tell apart (this is true for professional category, excluding self-employed tradespeople and shopkeepers) or the difference between them shrinks once territorial effects are introduced in the model (age). Indeed, the prevalence of foreign coins changes according to French regions. The probability of contact with a foreign coin is highest in Eastern France, on the borders with Germany and Luxembourg, and along the Mediterranean coast. Foreign coins are at their rarest in regions most distant from a border with a euro-zone country.
40Beside the effect of the relative proximity of the region to foreign countries, the fact of living in a municipality located at less than 50 km of a border with another country of the eurozone increases the probability to be in possession of a coin minted abroad. This result acknowledges the existence of integrated border areas in France.
41The international appeal of the Parisian agglomeration is reflected in a higher proportion of foreign euro coins than observed elsewhere in France. Interestingly, the urban hierarchy criterion does not have a linear impact on the probability of observing a foreign euro. The gap between Paris and rural municipalities (of under 2,000 inhabitants) is lower than between the capital city and towns of over 100,000 inhabitants. That counter-intuitive result calls for a more precise observation of the territorial nature of the distribution of foreign coins across France. Finally, in our last model we distinguished foreign coins according to the distance of their country of minting. It was found that this distinction did not change the nature and importance of the mechanisms behind the structural explanatory factors behind the overall presence of foreign coins in France.
42Once the factors behind the international circulation of coins were updated, it became possible to infer the presence of foreign euro coins across the country, so as to identify the most international places in France. Based on the estimates provided by the model integrating mechanical, temporal, social and territorial effects (see Annexes: Table 2—model III), we estimated the degree of European contact for each point of the French territory, which we then compared with the observed values. The maps shown in Figure 2 (see Annexes) allow to identify the places towards and from which contact occurs the most frequently between European residents.
- 10 It should however be noted that the appearance of a high probability “spot” in the Southern Paris r (...)
43Mapping the presence of foreign euro coins (see Annexes: Figure 2, Map 1) shows an uneven diffusion of foreign euro coins in France. We observe, on the one hand, the peripheries of the country as spaces with high potential for European integration (cross-border relations) and, on the other hand, the country’s main metropolitan areas, such as Paris, Lyons, Marseille-Nice and Lille10.
44Mapping of the residuals of the model (see Annexes: Figure 2, Map 2) also reveals some interesting results. It sheds light on the varying degrees of porosity of border areas, with foreign coins more numerous than predicted by the model around the Lille metropolitan area, close to the Luxembourg border, and at the feet of the Southern mountain regions, as these last are the necessary crossing points for Spain and Italy.
45Some large French urban areas also turn out to be more “internationalized” than their geographical position and population size would lead one to believe. This appears to reflect the city’s economic specialization (advanced services, international head offices and so on), which is the case of Lyon and Nantes, or its status as a university city, true of Rennes for example. A high number of foreign coins in a given location also denotes attractive tourist destinations, including the Mediterranean and Southern Atlantic coasts, Poitou and Northern Brittany (probably owing to the proximity of Mont-Saint-Michel, one of the most visited sites in France).
46These are just narrow hypotheses about the specific attractiveness of the places benefiting from the highest international circulation of coins in France. Undeniably, further researches have to be undertaken in order to shed light on the existence and causes of remarkable attractiveness of some cities at the European level and should be the subject of a dedicated article.
47Indeed, the primary objectives of this paper were to test the empirical relevance of using the circulation of euro coins to track the paths of individual mobility in the absence of data and to provide a general view of the spatiotemporal scales, motives and actors of cross-border mobility in Europe, thereby completing the existing sectoral approaches.
48For the same reason, this research only investigates the dichotomy of French vs foreign coins, despite the clear expectation that coins from different countries will be present in different quantities in different places. In a next study, we plan to segment our model into as many geographical origins as there are countries in the euro zone to reveal the territorial subsystems with the strongest interactions. Finally, our study focuses on one particular dimension of the Europeanization of territories and social groups in France: the movements of people. Obviously one could obtain a very different picture while looking at the flows of goods or financial flows.
49On the basis of our analysis, we conclude that the diffusion of foreign euro coins in France can be used to outline spaces and places of European mobility and, in particular, to show the uneven porosity of borders to transnational flows. It can also help to identify the metropolitan areas that are the most integrated in the system of European cities in terms of movements of people and to track down European tourists at a macro and meso-levels.
50To conclude, it appears that from monetary finds dating from Antiquity through to the introduction of the euro, currencies have always provided a relevant track of contact between people and the numerous paths connecting them.