A monocentric region is organised around a single strong centre that concentrates economic, political, and social activity (Bentlage et al., 2020). In practice, purely monocentric cities are becoming increasingly rare as urban areas expand and transform into polycentric or polysubcentric city-regions (Bentlage et al., 2020; Kebza, 2024). Examples of historically monocentric structures can still be found across Europe, such as the Paris or Munich regions, where centralisation formed the basis of current spatial structure (Bentlage et al., 2020; Desponds & Auclair, 2016).
The defining soil challenge for monocentric developments is one of concentrated pressure: a single urban mass that continuously attracts people, investment, and development. This places significant pressure on surrounding agricultural and open land, particularly at the urban fringe, where urbanisation frequently takes the form of sprawl. At the same time, concentration offers opportunities to limit dispersed development and support more compact use of land and infrastructure, for instance through greenbelts (Pourtaherian & Jaeger, 2022).
In monocentric regions, soil sealing tends to be most intense at the centre and to decrease radially outward, parallel to the gradient of built density (Bentlage et al., 2021). Within the core, decades of development may leave a legacy of compaction, contamination, and lost infiltration capacity. Yet concentration also creates opportunities to regenerate existing urban soils and invest systematically in inner-city green-blue networks. The monocentric region thus needs to strike a balance between preserving open spaces within the city and limiting its pressure on surrounding agricultural lands.
The most relevant planning concepts for monocentric regions are Smart Growth and the Compact City, which help accommodate growth while limiting land take (Perrott, 2023); Brownfield Development, which redirects investment towards already urbanised land (Loures, 2023); and Climate Change Adaptation and Resilience, which strengthens the role of green-blue infrastructure and permeable surfaces within dense urban environments (Birchall & Koleyak, 2023).
A polycentric region is organised around multiple urban centres that together function as a coherent system. Rather than one dominant core, functions, populations, and economic activity are distributed across nodes, connected by shared infrastructure and, ideally, by active regional cooperation (Zonneveld & Nadin, 2021).
The defining soil challenge of a polycentric region is one of managing the spaces in between. While urban pressure is distributed more evenly than in monocentric regions, the open land separating the nodes can gradually be consumed by sprawl, infrastructure, and low-density development (Barcelloni Corte & Viganò, 2022). At the same time, these in-between landscapes are one of the morphology's greatest assets, providing space for agriculture, biodiversity, recreation, water management, and ecological connectivity at the regional scale (Viganò et al., 2018).
Polycentric structures can reduce pressure on a single urban core and create a more balanced relationship between development and open space (Kebza, 2024). The presence of multiple centres offers opportunities to distribute housing, employment, and services while maintaining larger continuous landscapes than would be possible in a continuously expanding monocentric region. However, this balance depends on preserving the spatial distinction between urban nodes and the landscapes that connect them.
The most relevant planning concepts for polycentric regions are Regional Planning and Design, which coordinates development across multiple centres (Evers & Vogelij, 2021); Zoning, which helps protect strategic open spaces and agricultural land between nodes (Fischler, 2023); and Climate Change Adaptation and Resilience, which supports green-blue networks, ecological connectivity, and integrated water management across the region (Birchall & Koleyak, 2023).
A diffuse region has no single dominant centre and no clear hierarchy of urban nodes. Instead, urban and rural elements are woven together into a continuous, low-density fabric, with no sharp boundary between city and countryside. Land use is mixed throughout: residential, industrial, agricultural, and natural areas sit side by side, creating a diverse landscape where multiple functions coexist (Barcelloni Corte & Viganò, 2022).
The defining soil challenge of a diffuse region is, as the name suggests, diffuse: soil sealing and fragmentation happen gradually, in dispersed places, without a visible frontier. At the same time, the close relationship between urban, agricultural, and natural areas offers opportunities to rethink how soil, water, food production, biodiversity, and settlement patterns can support one another across the territory.
Of the three morphologies, diffuse regions tend to produce the highest soil sealing per capita (Pourtaherian & Jaeger, 2022). Discontinuous urban patches can fragment ecosystems and gradually consume agricultural and open land. Yet these territories also contain a rich mosaic of landscapes and land uses that can contribute to ecological resilience, local food systems, and climate adaptation when managed strategically (Barcelloni Corte & Viganò, 2022; Viganò et al., 2018). Because urban and rural functions are deeply intertwined, the challenge is not simply to contain growth, but to strengthen the relationships between urban and rural.
The most relevant planning concepts for diffuse regions are Agro-ecology, which strengthens the productive and ecological role of agricultural landscapes (Tornaghi & Dehaene, 2021); Regional Planning and Design, which helps reconnect fragmented territories; Zoning, which protects strategic open spaces and soil resources.
| Planning concept | Monocentric development | Polycentric development | Diffuse development | Relevant planning & design instruments LT: This should allign with the fact sheets. | | --- | --- | --- | --- | --- | | Zoning | Manages urban development by protecting both the urban fringe from outward expansion and the remaining open and permeable spaces within the urban fabric. | Protects strategic open spaces between nodes and prevents neighbouring centres from merging. | Uses environmental zoning to prevent fragmentation and protect agricultural and natural land from incremental development. | Inclusionary zoning, form-based codes, density bonuses, green belts. | | Regional Planning and Design | Coordinates the growth of a dominant centre and its surrounding transport networks. | Supports cooperation between multiple centres through network governance and coordinated spatial development. | Reconnects fragmented territories through territorial strategies that treat the region as a coherent system. | Regional design ateliers, metropolitan development frameworks. | | Climate Change Adaptation and Resilience | Mitigates Urban Heat Island effects and restores infiltration capacity in highly sealed urban areas. | Strengthens regional green-blue networks and integrated water management between urban nodes. | Manages open space as critical ecological infrastructure, providing water retention, biodiversity, and climate regulation services. | Sponge city approaches, nature-based solutions, green roofs, blue-green infrastructure. | | Brownfield Development | Regenerates compacted, contaminated, or degraded soils while reducing pressure for expansion onto undeveloped land. | Reuses degraded sites around urban centres and transport hubs to strengthen existing nodes rather than consume new land. | Transforms degraded sites into multifunctional landscapes, ecological areas, or productive land uses integrated into the wider territory. | Adaptive reuse, ecological restoration, IBA Emscher Park model. | | Agro-ecology | Uses green belts and peri-urban agriculture to connect the city with surrounding productive landscapes. | Preserves productive agricultural land between urban nodes as part of the regional structure, for instance through green fingers / green wedges. | Integrates agriculture as a central territorial function within a mixed urban-rural landscape. | Urban farming, agropolitan districts, Agronica-inspired approaches. | | Smart Growth and the Compact City | Promotes densification to reduce land take and improve infrastructure efficiency. | Directs growth toward well-connected nodes through bundled deconcentration and transit-oriented development. | Limits further fragmentation through clustered, low-impact, and reversible forms of development that minimise soil disturbance. | Urban growth boundaries, transit-oriented development (TOD), light infrastructure strategies. | | Participatory Planning and Design | Engages residents, planners, and soil experts in balancing urban development with the protection and restoration of urban soil functions. | Facilitates collaboration between municipalities, landowners, and communities to manage shared landscapes and soil resources between urban centres. | Mobilises local knowledge of land, agriculture, water, and ecology to guide soil stewardship across fragmented urban-rural territories. | Co-design workshops, living labs, charrettes, citizen science initiatives, multi-stakeholder platforms. |
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