This visualisation uses generally known divisions of a country. Administrative units account for many factors, such as natural borders, historical and cultural division, population density, utility etc. They define more or less homogenous regions of various shapes, sizes and several levels of detail.
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A country may be divided into provinces, which, in turn, are divided into counties, which, in turn, may be divided in whole or in part into municipalities. The data are aggregated through all those administrative units ad hoc in the platform. 

Click on any area in the map to get the detail about it. Using shift+click you can select several areas.  

If there's a link between data displayed in map and markers, you can click on any marker to display its "catchment area".