A GIS Tool for Transparent Real Estate Market Analysis A GIS tool to analyse real estate market has been built on MapInfo. Such a tool is of considerable potential value for real estate agents, valuators, consultants, facility management, construction industry, banking or even an accidental person having to make a transaction. The tool has these characteristics, some standard, some subtler: Search tools. There are standard search tools to find out the essential transactions (e.g. those needed in a comparative sales method) and characteristics of those transactions. A set of transactions can be found in several ways: by pointing on a map, by characteristics of transactions or simply by a list of numbers identifying the transactions. Thematic maps. The tool becomes more powerful as a set of thematic features is introduced. Most suitable attributes to be emphasized in a visual way are those measuring the volume and value of a transaction: floor space, unexpoited building right and unit prices of the two. Specifics for residential real estate market. The tool offers detailed information on market conditions on all phases of housing production chain: market for undeveloped land, market for housing lots and market for houses. The spatial interdependences are made visible. As there are more than a thousand annual transactions of residential real estate, a hedonic approach is also included: Statistical analysis. Standard statistical analysis is exploited measuring the impact of time and macrolocation on the unit price of housing lots, and the impact of those two plus age and size of building on the unit price of floor space of houses. A comprehensive model between market price and technical value of real estate is included. Spatial interpretation of hedonic models: The residual between actual and estimated prices are visualized, and thematic map reveals relevant phenomena on the impact of micro-location on the value of real estate. By simultaneous use of thematic mapping and hedonic analysis the tool offers a picture on real estate markets which captures the trends as well as the details, the picture being both illustrative and transparent. A case study of Helsinki Metropolitan area real estate market is presented, where the following submarkets are analysized: land for housing, single-family houses, industrial units and office/commercial units. Questions on access to data, price of data and other obstacles to transparency are also addressed.