Towards the ideal polity size: Population density as a solution for the trade-off in local democracy?

There appears to be a trade-off in the relationship between size and local democracy. Whereas smaller municipalities experience higher levels of political participation, they are simultaneously observed to have lower levels of political contestation. Based on this trade-off, it is impossible to identify an ideal population size at which both democratic participation and contestation are maximized. A solution to this problem could lie in the population density of a polity; a factor which so far has been understudied in the academic literature. A close geographical proximity between citizens may facilitate the creation of dense social networks, which could decrease the costs of information gathering, and may therefore effectively mobilize citizens to turn out and vote. As a result, population density may mitigate the negative effects of a large population size on turnout. Similarly, research indicates that population density may facilitate a more heterogeneous articulation of interests, potentially enhancing the positive relationship between a large population and political contestation. However, within municipalities of a small population size, the effect of population density on political contestation is still unknown. In fact, a higher population density in smaller communities may further intensify the dense social networks, which increases the social cost of dissent within smaller communities, and therefore lower the levels of political contestation even further. Based on these contradictory suppositions, this paper asks: Can the population density of a municipality resolve the trade-off in the relation between population size and local democracy? To address this question, based on a newly developed dataset, we look at the vote share of the largest party and voter turnout in municipal elections in European democracies between 1990 and 2020. By conducting a multi-level regression with a population density interaction effect, we examine the effect of polity size on voter turnout and electoral competition. Our contribution to the literature on size and democracy is two-fold. Firstly, based on cross-country comparative analyses, we provide new evidence about the effects of population size on voter turnout and electoral contestation in municipal elections. Secondly, we examine whether population density may stimulate both democratic competition and participation, potentially resolving the trade-off in the relation between size and local democracy.