The paper presents an analysis of generally available (open access) online sources of information – such as geoportals – in order to assess how valuable they are to the work of a real estate property appraiser. As a result of the analysis, it was determined what information is available in geoportals about a specific real estate property, which would be relevant in the valuation process. The property in question is located in the Dolnośląskie (Lower Silesian) region, Średzki district, Środa Śląska municipality. It is a property of a historic-cultural value. Two nation-wide geoportals were examined, as well as regional and local geoportals from the Lower Silesia region, where the valued object is located. Three categories of geoportal assessment were applied in this study, namely: functionality, transparency, and the availability of information about the valued property; the latter being the most important from the property appraiser’s point of view. The analysis showed that geoportals provide information relevant to the real estate property in the valuation process. The levels of information availability in the studied map portals were shown to have varied. Of course, this kind of information requires verification, because not all portals provide the date and time of the last information update. That notwithstanding, they still constitute valuable sources of information about the real estate property.