Urban patterns

Scira Menoni and Funda Atun (POLIMI)

Cities’ complex interdependences between elements and systems occur in the three dimensional space. An urban pattern is the combination of buildings’ density, the prevailing typology of the road network, i.e. ring, grid or linear, and the width of the streets in comparison with the height of the buildings and, finally, the features of the natural environment, that constraints and in the meantime provides opportunities for cities’ development.

The type of urban pattern has decisive implications for emergency management, and in particular for all activities related to evacuation, positioning of roadblocks, selection of areas devoted to locate civil protection and rescuers tracks and devices. A regular grid, such as that characterizing the original roman-style settlement can be easily found in colonial cities, in modern expansion areas such as in Volos in Greece and sometimes also in ancient towns such as Turin in Italy. Such regular grid guarantees redundancy in access ways to almost all point shaped element in cities and fastest in and out travels. Furthermore, the regular grid permits to better define areas pertaining to predetermined emergency centres and to distribute rationally services such as hospitals, fire brigade stations, etc.

Circular, round grids are more complicated to manage: redundancy is still guaranteed but not to all locations, avoiding central nodes is virtually impossible, congestion is more likely in ordinary times and to be expected and therefore carefully managed in emergencies.

Linear cities are those that develop along the coast or important infrastructures such as roads and railways; they are characterized by the general absence of significant alternatives in case of transportation routes failures and by the fact they are easily cut in more parts disconnected from each other that will need to respond a crisis independently from each other. This was certainly the case in Kobe, Japan, a rather emblematic example of linear city, hit by the earthquake in 1995.

Whilst cities generally present a predominant pattern, there may be also coexistent patterns, particularly in large metropolitan areas that result from the aggregation of pre-existing settlements once autonomous and of newly added development zones.

Different city patterns require city and disaster managers to adopt different strategies in deciding the location of critical infrastructures, in defining self reliant zones and in preparing themselves, other agencies and citizens for contingencies.

The street pattern in Lorca, Spain

Lorca contains both organic and linear patterns in its street morphology. The city was organized on a human scale, and is highly walkable. It provides a low speed of travel within the narrow streets and a high speed of travel in the recently built linear pattern.

The street pattern in Istanbul, Turkey

The pattern is taken from a residential section of Istanbul. The area includes a mono-functional housing development that does not provide functional feasibility. However, the distribution of the streets provides accessibility.

The street pattern in Volos, Greece

Volos has a grid street pattern that provides a rapid connection between distant parts of the city. It is highly accessible. Urban blocks are mixed-use, combining residential, touristic and commercial activities.

However consideration cannot be limited to the plan layout: buildings, transportation networks, services, work activities occur in three-dimensional space. The relation between the latter needs to be considered also vertically. In the 18th century for example, scholars and architects were already aware of the fact that the reciprocal ratio between the height of buildings and width of streets has important implications in case of earthquakes, determining the possibility or not of buildings standing at the opposite sides of a street battering against each other; they were also concerned about the amount of debris that could layer on the road, provoking its closure and the difficulty to open it rapidly for search and rescue. We may certainly say that such relationships are relevant also for other risks, such as floods, in determining for example the time needed to dry up first floors after inundation.

The urban pattern in the third dimension also has relevant implications during emergencies, as it implies the ease of carrying and using cranes if necessary, of maneuvering fire trucks, etc. In modern times different interventions can be thought of, provided that such relationships are recognized and related to a variety of indicators of health, sustainability and safety as for the built environment, whilst considering appropriate dimensions of emergency cars and devices to be used in constrained environment.

The streets of Orvieto a historical town in Umbria Region (photo credit: Claudia Moreschi)
A main street in Istanbul Metropolitan City

People’s use of buildings and spaces

How people use places and buildings depend on their culture, there is the indigenous culture of the inhabitants of cities but also the newer inhabitants bring their own ways of using space (for example public spaces). Uses may be or become incompatible with the original layout of buildings requiring changes in internal configuration of spaces that may lead to unpredictable yet dramatic outcomes in terms of structural resistance to earthquake. For example the opening of large shop windows at the first floor of buildings, or the elimination of structural components to create parking spaces or laboratories may change the original performance of buildings against horizontal accelerations.

The use of basement as residential units or offices clearly puts at risk the life of people and valuable goods in flood prone areas. City managers need to be aware of the fact that not only hard components of cities determine structural features, but also the soft way spaces and artefacts are exploited and changed to better conform to new uses.