4.1.1. Densification

In general, densification strategies seem to encourage different typologies of urban development (e.g., compact, polycentric). The results of the intervention database show that densification types of interventions, which promote up-zoning and in-fill development mechanisms, are usually successful in encouraging more sustainable urbanization processes.

Certain characteristics, such as the adoption of long-term sustainable aims and objectives, seem to support the effectiveness of these types of strategies. This can be seen in the Croatian Spatial Plan of Primorje-Gorski Kotar County (available at: https: //zavod.pgz.hr/en/plans\_and\_reports (accessed on 15 March 2021)), which aims to limit future urban growth by promoting a more effective managemen<sup>t</sup> of land use. To limit urban growth, a number of criteria for determining the size of building areas of settlements, regulating population density, were set. For example, the maximum surface area of building areas in each municipality was derived from the projected population and

the minimum density of the inhabitants of the urban area. However, the intervention also seems to have had negative effects since, in an attempt to limit future urban growth, non-residential facilities seem to have been driven further away. Thus, it is important for the local administrations to adopt tangible and short-term objectives when trying to promote a long-term sustainable development.

Other characteristics, such as an increased cooperation between the various stakeholders, also seem to improve the effectiveness of these interventions. For example, the success of the Royal Seaport eco-district in Stockholm (Sweden) is attributable to the constant dialogue and negotiation between the various actors (e.g., public and private) during the various phases of the project. The project shows how the City of Stockholm (which has limited space for greenfield development) has managed to promote densification measures in order to be able to accommodate population growth, as well as to find the most effective environmental solutions [32].

The implementation of legal binding instruments often seems to improve the successfulness of these types of interventions. This is the case of the general development plan of the City of Stara Zagora and its adjacent territories (Bulgaria). For the expert reporting this intervention in the survey, it is one of the most effective tools to fulfil its limitation functions. In fact, the objectives and targets of the plan, including the upper limits of the development indicators, are compulsory and the failure to comply with them is illegal.

Data, knowledge and technical capacity are other characteristics that seem to promote more effective sustainable development. For example, the Infrastructural Cost Calculator, a strategy set up in the region of Lower Austria (Austria), supports municipalities in pre-assessing the financial costs (e.g., municipal infrastructural costs and tax revenues) of urban expansion and related population increase [33]. Thus, the strategy tries to assess the municipal consequences on where and how new inhabitants are settled. However, the effectiveness of the intervention seems to vary in relation to its implementation and a certain level of discretionality seems to characterize its implementation.
