The Geographic Information Systems (GIS) are becoming a major tool in the domain of geological hazard assessment and risk mitigation. When available, hazard and vulnerability data can easily be represented in a GIS and a great diversity of risk maps can be produced following the implementation of specific predicting models.

A major difficulty for those that deal with GIS is to obtain high quality, well georeferenced and validated data. This situation is particularly evident in the scope of risk analysis due to the diversity of data that need to be considered.

In order to develop a coherent database for the geological risk analysis of the Azores archipelago it was decided to use the digital maps edited in 2001 by the Instituto Geográfico do Exército de Portugal (scale 1:25000), comprising altimetry, urban areas, roads and streams. For the particular case of S.Miguel Island the information contained in these layers was revised and rectifications were made whenever needed. Moreover basic additional layers were added to the system, including counties and parishes administrative limits, agriculture and forested areas. For detailed studies all the edifices (e.g. houses, public buildings, monuments) are being individualized and characterized taking in account several parameters that can become crucial to assess their direct vulnerability to geological hazards (e.g. type of construction, number of floors, roof stability).

Geological data obtained (1) trough the interpretation of historical documents, (2) during recent fieldwork campaigns (e.g. mapping of volcanic centres and associated deposits, faults, dikes, landslides) and (3) by the existent monitoring networks (e.g. seismic, geodetic, fluid geochemistry) are also being digitised.

The acquisition, storage and maintenance of all this information following the same criteria of quality are critical to guarantee the accuracy and consistency of the GIS database through time. In this work we notice the GIS-based methodologies aimed to assure the development of a GIS database directed to the geological risk analysis in S.Miguel Island. In a long-term programme the same strategy is being extended to the other Azorean islands.