Volunteered Geographic Information (VGI) represents a valuable source of information. At the same time this data presents new data quality issues such as credibility. In this paper, we investigate the integration of VGI in Spatial OLAP (SOLAP) systems, which allow analyzing huge volume of geographic datasets. By means of a real case study, we highlight the similarities and differences of these two kinds of systems. We propose a methodology to handle VGI data quality issues during the warehousing and OLAPing phases. In particular, we define a new aggregation ETL operator based on the VGI credibility. We also present a spatio-multidimensional model that provides decision-makers with a general description of the correctness of the SOLAP aggregations.