AbstractA new realm in spatial planning defies administrative boundaries and adopts larger territories than cities, which encompasses city clusters where cities can both compete and cooperate rather than compete as individual entities. In that regard, various approaches to the delineation of functional regions and “mega” regions have been proposed in time, based on population and employment, the urban landscape, or the interactions between regions in terms of intracity travel or migration flows. This paper proposes a methodology to delineate functional regions as well as megaregions based on the pattern of intercity freight flows and a composite economic indicator, exemplified by a case study of Turkey. A four-step delineation method is proposed in which population and trips are used initially to rank the cities and their hinterlands. Second, hierarchical clustering is carried out to delineate new clusters based on flows, and the resulting clusters are used to delineate functional regions for regional planning purposes. Third, a composite economic indicator (income and wealth index, IWI) is employed to refine and finalize the boundaries, thus ensuring the functional zones’ homogeneity as economic clusters. In the last step, megaregions are pinpointed based on the cities of the functional regions using two criteria: IWI (≥0.4089) and GDP (TRY ≥18.3 million) in 2015. The defined regions represent a new geographical scale in regional planning that can aid the central government in addressing leading regional issues: for example, prioritizing governmental investments that are subsidized by national funds aimed at the alleviation of regional inequalities. A future study may focus on the effect of regional economic inequalities on internal migration flows.