Planners and decision - makers involve with a variety of activities undertaken at different spatial scales by national, regional or local organizations. They have to be aware of new techniques surrounding them. Geography Information System (GIS) is a set of computer sciences which can help planners in different areas such as housing, industry, environmental management, urban planning and so on. In this study the following titles, the object of GIS, types of data storage, hardware and software in a GIS environment, type of information systems, and application and user of GIS will be discussed.

Proper stream network mapping is highly needed for any hydrological studies particularly for automatic flow routing in GIS based raster models. Generally, one of the disadvantages of making use of digitized stream network, based on topographic maps is incompatibility of stream features with flow direction vectors. In an uncertainty condition, making use of this stream network will terminate routing program before normal ending. An algorithm was designed, making use of Avenue program in Arcview GIS. Designing this algorithm was based on D8 method, which is one of the pixel to- pixel flow conduction methods. Points lying on digitized stream network can get elevation in a vector domain. Then, these points can be used in determining stream flows, which produces new stream network of catchments. The new generated stream network, in spite of having vector property, exactly coincides with flow direction patterns. One of the most important specifications of this algorithm is reallocation of stream network without generating extra features.

GIS provides an excellent means for visualising and analysing epidemiological data, revealing trends, dependencies and inter-relationships. It can acquire, store, manage, and geographically integrate large amounts of information from different sources, programmes and sectors. GIS serves as a common platform for the convergence of multi-disease surveillance activities. Standardised geo-referencing of epidemiological data facilitates structured approaches to data management. Once the basic structure is ready, it is easy to convert it to a surveillance system for any other disease. Public health resources, specific diseases and other health events can be mapped in relation to their surrounding environment and existing health and social infrastructures.GIS helps generate thematic maps that depict the intensity of a disease or vector. GIS can identify catchment areas of health centres and also locate suitable sites for a new health facility. GIS allows interactive queries of information contained within the map, table or graph. It permits a dynamic link between databases and maps so that data updates are automatically reflected on the maps. Dynamic maps published on the Internet assist patients in locating the most convenient health services easily.

Landfills are potentially seriously pollutant areas. It is therefore necessary to prudently locate landfills in the periphery of the city to prevent potential ecological and hygienic hazards. A system linking various data to spatial location, GIS can be a useful tool in this area. The factors affecting the location of a landfill include: typography, climatic conditions, geology, water resources, adjacent land use, economical and aesthetic factors, as well as access to infrastructure. The appropriateness of a certain site with regard to these factors can be determined using Boolean operators. This paper describes the process of and an algorithm for determining appropriate sites for landfills using GIS.