Coordinate-based mapping--a new method in health services research.

The Finnish national hospital discharge registers from 1985 and 1988 have been analysed by the National Board of Health. Results are provided for all the 21 Finnish hospital districts and central communal organizations. The small area variation phenomenon in hospital utilization cannot be explained by demographic or epidemiological factors. Rather, the variations seem to be largely due to organizational factors. The project aims to develop a data processing system capable of handling information on one million patients rapidly and economically, and show the results in an intelligible form as a table with standard headers or as a map illustration. Maps are superior to traditional statistical tables in demonstrating regional variations in health care utilization and in mortality. Maps based on small administrative units are useful for many purposes. These maps are, however, relatively 'noisy' due to substantial random variation. Coordinate-based mapping is a method to overcome some of these difficulties. It is based on linking hospital discharge and mortality data with exact address data. The method allows mapping independent of administrative boundaries. Several examples of coordinate-based maps are given. The method is used in Finland for annual analysis of hospital use.