Abstract
The Chalcolithic Age is one of the most important prehistoric periods in Iran. The transformations of this period in the Central Zagros have emerged in continuation of the Neolithic period.  One of the important areas of Central Zagros, which had many settlements related to the Chalcolithic era, is Silakhor plain in the north of Lorestan. Despite the cultural richness of the Silakhor plain during the Chalcolithic Age, no purposeful study has been conducted to clarify the Chalcolithic status of this area. In this regard, in order to clarify the settlement models of the Chalcolithic era of Silakhor plain, this study is presented, which is a summary of Ahmad Parviz’s archaeological studies and purposeful studies by the researchers, In the present study, the authors have tried to find the answer to the following questions: What were the settlement models of Silakhor plain in the Chalcolithic era? How can the changes of settlement models in the old, middle and new periods of the Chalcolithic era of Silakhor plain be analyzed? It seems that several factors including water resources, altitude of Silakhor plain and state’s roads have been effective in the formation of settlements in this area during the Chalcolithic age. Studies conducted in this plain so far have shown 80 ancient sites related to the Copper Stone Age. Some of these sites involve all three periods of old, middle and new Chalcolithic era. The spatial data collected in this research have been studied by GIS science studies method and implemented in ArcGIS 10.3 software. The basis of these studies is the distance of each settlement area from the nearest river and its altitude level from Silakhor plain. These maps have been implemented in all three periods of old, middle and new Chalcolithic Age of Silakhor plain. 
Keywords: Central Zagros, Silakhor Plain, Chalcolithic Age, Settlement Models, GIS.

Introduction
The Chalcolithic Age (mid-fifth millennium to late fourth millennium BC) is one of the prehistoric periods which has witnessed important transformations such as population growth, enhancement of the quality of pottery, the use of copper metal, improvements in the quality of settlement construction and so on.  Some scholars consider this period to be a continuation of Neolithic transformations and some consider it as being independent of other periods. Archaeological studies conducted over the past few decades in the Central Zagros region have shown that this area has seen an increase in population during the Chalcolithic period. This increase in population is inferred from the number of archaeological sites recorded in this period compared to the previous period (Neolithic). Of course, the studies indicate that archaeological studies conducted in connection with the Chalcolithic Age of the Central Zagros, have focused mainly on the Gamasiab River Basin.
Silakhor plain has a suitable situation geographically and climatically.  The flat plain and fertile soil along with sufficient water resources have caused us to see a large number of ancient sites from the Neolithic period to recent centuries. Despite the conducted studies, so far no purposeful studies have been conducted to analyze the residential and settlement situation of the Chalcolitic era of Silakhor plain. In this regard, the researchers, while exploring the studies conducted in this plain, have re-examined the ancient sites of the Chalcolithic era of this plain. Since the area of Silakhor plain is located in Boroujerd and Doroud counties and covers a large part of the north of Lorestan province, in this research, this plain is divided into two parts, north and south, the northern part of which is in Boroujerd and the southern part is in Dorud city. In order to study the situation of the settlements of Silakhor plain more accurately, its northern part in Boroujerd city has been chosen. 

Findings
The chronology of the Chalcolithic age of Silakhor plain and the east of Lorestan is also influenced by the chronology of the Gamasiab river basin and the Kangavar valley. The study and identification of the archaeological and historical monuments of this area has been done recently by Ahmad Parviz in 2006 and the review of the researchers in line with this research has been done in 2016.  In this study, according to Godin chronology, areas related to the chalcolithic age during three periods of old, middle and new era are studied. Sites are evaluated by the ArcGIS 10.3 software after being located on elevation maps through their Universal transverse Mercator (UTM).  In this evaluation, the altitudes of the area compared to the average altitude of the northern half of Silakhor plain and also their distance to the nearest rive, are examined. In the studies performed, it has been determined that 80 sites are belonged to the Chalcolithic age of the northern half of Silakhor plain, some of which include all three periods of old, middle and new Chalcolithic era.
 Of all 80 Chalcolithic Age sites in the study area, 25 sites are related to the old period. These areas are mainly distributed in the central parts and in the plains.  Most sites are at altitudes between 1,500 and 1,600 meters above the sea level.
Of the 80 Chalcolithic Age sites in the study area, 31 sites are related to the Cenozoic Ages. These sites, like the old period, are mainly distributed in the central parts and in the plains. Most sites are at altitudes between 1,500 and 1,600 meters above the sea level.
Of the 80 Chalcolithic Age sites in the study area, 42 are related to the Cenozoic period. These areas, like the old and middle periods of the Chalcolithic Age, are mainly distributed in the central parts and in the plains. Most sites are at altitudes between 1500 and 1600 meters above the sea level.

Conclusion
In this study, it was found that the number of old, middle and new sites of the Chalcolithic Age in the northern half of Silakhor plain (Boroujerd) are 25, 31 and 42 , respectively. This indicates that the Copper Stone Age in this area has developed in a growing trend (in terms of the number of settlement sites). Increasing the number of settlements in this area paves the way for future transformations in the next period (Bronze Age).  Therefore, the beginning of urbanization in this area has had a strong and evolving introduction to the Chalcolithic era.
On one hand, the study of maps prepared in ArcGIS software shows that the vast majority of sites in all three periods in the Chalcolithic Age are located at an altitude of 1500 to 1600 meters (average height of Silakhor plain is 1500 to 1600 meters) and in the area of Silakhor plain.  On the other hand, the analysis of the distribution map of the Chalcolithic sites of this area shows that the settlements of this period have been formed depended on the water resources (rivers).