Analysis of the urban growth pattern through spatial metrics; Ankara City

In the industrialization that started in the 1830s in countries such as England and America, transportation networks, geographical locations and spatial size were taken as the basis in the selection of the industrial city. Within the scope of this approach, the industrial sector was created in the city periphery and the cities expanded spatially by being exposed to rapid job migration. The form of engagement of cities to industry in this way became a strategy of nation-state policy in the 1920s in Turkey. Within the scope of this strategy, Ankara, which is at the center of the railway network, was declared as capital; manufacturing industry, private sector and public investments in the city were strengthened and the city was exposed to job migration. Along with industry, marginal changes in production and market form have led to population clustering and spatial expansion in urban areas. Spatial expansion in cities has also been affected by land use policies as much as the city is affected by the functions it gains in the industrialization process, and a multidimensional structure has emerged in cities, in which different actors interact at different spatial scales. Urban sprawl and compact development, two of the forms of spatial growth, which are an important result of this structure, have been discussed since the 1980s. This study evaluates the change of urban growth pattern and the land use policies that caused this change in Ankara, which is the capital of Turkey and the second largest city in terms of population, based on the acceptance that urban growth is a multi-component and multi-factor phenomenon. By analyzing (LULC change, density gradient analysis, configuration and composition analysis, urban growth density analysis) multi-time (1984–1992–2001–2009–2018) and multiscale data sets (Landscape level, Class level, and Circle Direct Zone level) with spatial metrics, these land use policies need to be determined more clearly. Urban growth takes shape in different models. In order to determine different urban growth models in sub-scales such as neighborhoods, direction and distance variables were included in the analyzes and thus land use decisions that feed the urban growth trend at different scales were determined more clearly in this study. It has been determined that spatial metrics can have very good results in determining urban growth patterns and landscape change dynamics. Within the scope of this study, EROPA (Effect Ratio on the Peripheral Area of the Urban Area) index, which explains the urban growth pattern, was developed. The EROPA index consists of the combination of landscape indices and Shannon’s entropy index and provides the opportunity to determine the urban growth pattern with a single index. The obtained results provide important insights in the development of the city's land use strategies. Land use decisions in Ankara encourage urban growth more in some regions and population density accelerates with this incentive. The city of Ankara became compact in all directions in the 10 km area surrounding the main city center between 1984 and 2018, and after the 10th km, there is a tendency to spread in all directions, but it has been determined that the tendency to spread is especially higher in the west direction. Therefore, population agglomeration formed in the west direction in those years. Between 2009 and 2018, population growth in the region between the 13th and 32nd km in the west corresponds to 48.5% of Ankara's total population growth. Due to the establishment of commercial and small-scale business areas at the periphery, the influence of spatial planning decisions and the dependency (neither far nor near) on the Central Business District (CBD) in the main city, the shape of the settlement patches formed by the increasing urbanization trend from the main city center to the periphery is irregular and complex. The proportion of the main urban core in all urban areas decreased from 61.33% to 46.99% between 1984 and 2009 and increased to 55% of the total urban area between 2009 and 2018. The growth trend in edge-expansion increased from 40% between 1984 and 1992–56% between 2009 and 2018. This type of growth accounts for approximately 66% of all growth between 1992 and 2001. 1 km2 of urban area affected 1.29 km2 of peripheral open area in 1984, while it affected 1.01 km2 of peripheral open area in 2018. These values show that the effect of the urban area on peripheral open areas has decreased over the years in Ankara; in other words, the urban patches have approached each other over the years and the patch shapes have become smooth in Ankara. The analysis and spatial metrics used in the study provide clear information in identifying and interpreting the land use dynamics of urban growth, urban growth tendency and urban sprawl types, and these analyzes and metrics have been found to be an important tool that can bridge an important gap and prevent urban sprawl problems.