The use of GIS for various types of data is considered to be of high importance, mainly because it is bringing together information from multiple sources. In addition, the new Internet technologies and applications of global world maps, like Google Maps, give the opportunity to build systems that the geographical information can be recorded and administrated by many users from anywhere. This kind of GIS systems is suitable for Business Administration, or Science, or Government Organizations, which need GIS systems with multiple users from many places and multiple kind of information. This system is defined as GISΜΑ (Geographic Information System Multi Administration). In GISMA many users may input the data and use the information from different distance. Each user has specific permissions of use of data as the administrator sets. In this work, the basic principles and rules of a building GISMA system are evaluated and an application is presented based on data and GIS techniques for the slope instability studies. Data obtained from historical landslide occurrences were verified with new locations obtained from high resolution orthophotos and Google Earth application. Landslide areas were mapped using Arc Map and finally the Landslide Inventory for the Achaia’s Prefecture was created.