Urban management in a city with so many growing problems is a never-ending difficult task (Nkurunziza, 2007, 5؛ Abbott, 2000, 8). Along with the growing perception of the role of cities in the international development throughout the world, one can see the disability of governments to provide the needs of peoples. Indeed, the economical success of governments depends of the successful management of cities. Therefore there should be a new management method which by integrating different fields improves the efficiency of the management. Nowadays one of the well-known management systems is geographical information system. This system has a special role in many urban activities, management and urban planning. With the capability of GIS in gathering spatiotemporal data, management, analysis, retrieval etc. studies of historical data are easily achievable.
Misunderstanding and insufficient understanding of the urban systems and future expanding mechanism of cities are among the main reasons for the failure of many of management activities and urban planning in developing cities which brings about disorder and informal settlements (Abbotte, 2002, 3). By using geographic information system, one could easily understand urban dynamics and evaluate circumstance of physical development (Sietchiping, 2003a, 2).
Nowadays informal settlements are among the main problems in many of the developing countries. For efficient management of these places one of the ways is to know, evaluate and forecast trends of development at different times. The case-study in this research is the city of Ahvaz. Ahvaz is a metropolis with 8 official districts. From spatial point of view it is constructed of crossed system. Non existence of natural element, plantar coverage and high topography has made accessibility network, constructions and buildings to develop widely and disorderly. Marginal expansion of the city caused some rural part be connected to the city and cross the official boundary which in turn has attracted many immigrants. Finally, these places with aimless planning join the city. This city is a metropolis whose main portion of its population has resided in informal settlements. Considering the existing poverty in this city, 17 sectors can be determined as informal settlements (Ahvaz Informal Settlement Studies, 1385, 68). This study then seems to be essential for improving and managing and control the rapid irregular expansion (Taghizadeh, 1387, 30).
In order to achieve the main objectives of this research different types of data have been gathered. According to their type data are classified into three groups:
1- Official boundaries data;
2- Generally and formally proposed and land- use data; and
3- Remote sensing images that include TM (1991) and ETM (2002) data's.
After collecting each data and considering its primary states they are processed and adjusted to be ready for importing into analysis. For example city boundary data are first scanned and then after geo-referencing are imported into ArcGis9.3 and then are digitized. Some of generally proposed data were in DWG format and the others are scanned maps. For improving the accuracy and reliability of these data they are controlled and refined by using IKONOS satellite images. The last group (remote sensing) data are also controlled and refined by using IKONOS image because all the data have the same spatial accuracy and precision.
In practice, the general trend of expansion of the city was analyzed first and then this was also applied to land - use maps which derived from remote sensing and the city land-use maps. After analysis the results of each type of data are compared to recognize the main aspects of development. The city boundary map in the years 1364, 1374, 1385 gained and compared to each other to analyze the rate and total directions of development. For this reason, area of expansion in the periods 1364-77, 1374-85, 64-85 is gained and the portion of each direction is calculated. Comparison of areas in each direction shows that the general trend of expansion has headed towards the south, north and north western directions.
Remote sensing data; such as the city boundary maps are also analyzed; and finally, by comparing different maps in some periods the portion of each direction from expansion is calculated. Before doing this experiment by using remote sensing data some extra operations like reconnaissance, choosing training points, analysis of group classes and classification were also done. Comparison of residential districts by using remote sensing images, in two periods of 1991 and 2001 shows that the North eastern, south and north-western directions had the most portions of expansion.
General projection and formal projection maps in period of 1364 to 1374 are also compared and the results show that north western, south western and south directions have the most expansion. By looking at each map individually, one can see that the dominant directions of expansion are not exactly the same as result of the total comparison in two years (1364 and 1374). This conflict means that the area can not individually show the accurate direction of expansion, and ratio of increase should be considered.
Comparison of results in all data shows that the Northeastern, South and Northwestern are the dominant directions of expansion. despite some natural preventive factors in development directions, they have expanded. This shows the fact that there is no firm limitation, especially official one, in these areas. In accordance with rapid settlement growth in these directions, as result of total population growth, urban planners and managers should immediately adopt new approaches to control this issue.
The research’s suggestions are: Creation of green belt, legal prevention of informal settlement and moving them to other areas, planning for these areas should be in priority; and Creating new towns in this direction and supervision on construction and land development.