Building Consistent Territorial Units over Time: A Graph-Based Method for Historical Municipal Boundaries in Italy

Paolo Buonanno, Bianca Cattaneo, Giampaolo Lecce, Vitantonio Mariella and Laura Ogliari

No 20714, CEPR Discussion Papers from Centre for Economic Policy Research

Abstract: Administrative boundaries rarely remain stable over time, yet quantitative economic history often treats local units as fixed. As a result, mergers, splits, and redefinitions can generate spurious breaks in historical series and bias long-run analysis. We introduce a general method to construct time-consistent territorial units (TCTUs): municipalities are represented as nodes in a dynamic network linked by documented events, from which stable aggregates can be extracted for any user-specified interval. The method ensures historical comparability while preserving the finest feasible spatial disaggregation. We implement it for Italy, reconstructing the complete history of municipal transformations since unification using official ISTAT records. Applications illustrate how ignoring boundary changes can produce misleading evidence of demographic decline, whereas TCTUs recover coherent trends. A companion open-source tool provides the code for Italian municipalities and can be adapted to other contexts with detailed administrative histories.

Date: 2025-10
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