The relationship between city size and territorial productivity has
attracted much attention in the urban economic literature. Some theories on the
field claim for a strong positive correlation between the size of the municipalities
and their income, mainly motivated by economical reasons, geographical characteristics
or other factor of the urban environment. Unfortunately, in many countries the empirical research on this topic is not possible given the lack of data of income
at a local level. This paper proposes the use of entropy econometrics to estimate
urban income and urban productivity according to city size from aggregate information,
which can be defined as an exercise of ecological inference. With the estimated
data a regional classification based on the relevance of the cities size allows
us to measure the relevance of agglomeration economics on the cities productivity
in Spain.