Patents heatmap
Where did inventors of mechanical calculating devices live?
This map shows locations (at the city level) of inventors and assignees of patents for mechanical calculating devices. One patent can contribute several locations. Because old patents can contain place names that are not recognized by Google Maps, latitudes and longitudes of the places mentioned in the patents are checked against the Getty Thesaures of Geographical Names (yes, this is tedious work).
Open the distribution per country
See the Rechnerlexikon for extensive patent information on mechanical calculating devices.