The built environment is a product of socio-economic, cultural, and political forces. Every urban system has its own 'genetic code', expressed in architectural and spatial forms that reflect a community's values and identity. Each community chooses certain physical characteristics, producing the unique character of its city. This 'communal eye' exemplifies the city's architectural legacy and gives a sense of place. 

For example, in old Sana'a, the capital of Yemen, unique buildings decorated with geometric patterns create a distinctive visual character unique to the city (pictured above). Another example is Egypt's Nubian village (below) where the building materials and colors  are unique and reflect the vernacular architecture of the region.

However, current architectural practices, in almost every city in the world, do not respect the past identities and traditions of our cities. Most projects bear little or no relationship to neither the surrounding urban context nor the city's genetic code. Architects only follow international architectural movements such as "Modern architecture", "Postmodernism", "High-Technology", and "Deconstructionism". The result is a fragmented and discontinuous dialogue among buildings, destroying a city's communal memory.     

Street art and graffiti have been filling this gap, explaining the conflict between the traditional culture and contemporary sociopolitical issues of cities. Street artists are repurposing city walls to highlight heritage, history and identity and, in some cases, to humanize this struggle. Each city has a unique wall art that has become part of its overall genetic code. Some of art in Santiago (pictured below), for example, highlights Chilean identity. Another example is how wall art was used during the Egyptian revolution to memorialise the events. In March 2012 young graffiti artists launched the "No Walls" movement when the Egyptian authorities constructed a number of concrete walls to block important street junctions so as to control peaceful demonstrations. 

Bill Hillier, a professor of Urban Morphology, offers a different interpretation. He suggests that the street network of any city is made up of a dual network ?the foreground network, consisting of the main streets in the urban system, and background network, made up of alleyways or smaller streets. The foreground network, or the main street network, usually has a universal form, a 'deformed wheel' structure composed of small semi-grid street pattern in the center (hub) linked with at least one ring road (rim) through diagonal streets (spokes). But the form of the background network differs from a city to another; therefore it is this network that gives a city its spatial identity.

Many cities such as London, Tokyo, and Cairo have a similar universal street pattern of a 'deformed wheel' in foreground network in spite of having different background networks, possibly as a result of cultural differences or contributing to the creation of those cultural differences. In short, the background network reflects the unique structure of each city, and could be considered its genetic code.

However, in my view the the background network alone is not enough for representing the genetic code of built environment. Architects and planners must look up from the grid of the ground, respecting local architectural, spatial and cultural dimensions. Citizens and architects should work together to restore a sense of local identity in a contemporary idiom. Community participation programs as well as developing design guidelines that are sensitive to each city are the only way to maintain a city's DNA. A healthy and well-functioning city is similar to the human body: it is important to maintain its genetic code.

Abdelbaseer A. Mohamed is a short-term scholar at American University in Washington DC and a PhD student at Ain Shams University, Cairo, Egypt.  

Images via Rod Waddington, Chris Brown and Antunno Ruggero.