OpenStreetMap Nominatim Centre Point – Is It the Centroid and What EPSG Is It?

epsgnominatimopenstreetmapweb-mercator

I looked up a couple of places on OpenStreetMap's Nominatim, like Bruck an der Mur, and I could not confirm whether the reported coordinates are indeed the same thing as the centroid, and which EPSG is used. I recall that Web Mercator (EPSG:3857) is used for online mapping tools, such Google Maps and OpenStreetMaps. However, given that this "Centre Point" is lat-lon, I am inclined to believe it's EPSG:4326.

What is the correct one?

Best Answer

Nominatim is using OpenStreetMap data and the boundary of Bruck an der Mur is this OSM relation https://www.openstreetmap.org/relation/3904390. The named place is this OSM point https://www.openstreetmap.org/node/34855256. It is not computed by the boundary as centroid or point on surface but the OSM mapper "JM82" has placed the town centre just there. The source data as XML reveals the latest editor as well as that natively the coordinates are stored into the OSM database as latitudes and longitudes.

<osm version="0.6" generator="CGImap 0.8.5 (2187694 spike-08.openstreetmap.org)" copyright="OpenStreetMap and contributors" attribution="http://www.openstreetmap.org/copyright" license="http://opendatacommons.org/licenses/odbl/1-0/">
<node id="34855256" visible="true" version="9" changeset="59510747" timestamp="2018-06-03T14:44:55Z" user="JM82" uid="2641694" lat="47.4121987" lon="15.2721668">
<tag k="name" v="Bruck an der Mur"/>
<tag k="name:hu" v="Bruck an der Mur"/>
<tag k="name:ru" v="Брук-ан-дер-Мур"/>
<tag k="place" v="town"/>
<tag k="population" v="9748"/>
</node>
</osm>
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