The OpenData initiative of the city of Vienna (http://data.wien.gv.at/) has released a dataset about all fire hydrants of vienna. On the 17th of April it contains of 12702 unique entries and no additional attributes.
One can see that the area of Vienna is completely covered. The dataset itself seems to be quite accurate.
In OpenStreetMap, a fire hydrant is marked with the tag “emergency=fire_hydrant”. When filtering the OSM dataset of Vienna from the 16th of April the following hydrants (blue dots) are revealed:
The sum of all fire hydrants in the OSM dataset was 67. They are not placed as dense as for example trees, therefore it is easier to find out which of the fire hydrants in the OGD dataset should not be imported.
Preparing for Import
A quick analysis revealed that with a buffer of 20 meters, most of the already mapped fire hydrants (63) can be detected and omitted.