Geocoders Comparison Update
Comparison of four geocoders: Nominatim, GoogleV3, ArcGis and AzureMaps
Geocoding services (via Geopy):
Geocoding refers to the maping of an address to its geographic coordinates. Specifically, the geocoding of a location specified by a query string can be achieved using calls to geocoding services (APIs) directly in a browser address box, or with a wrapping library such as Geopy.
Why I setup this comparison:
In another application, I tried using the New York City boroughs bounding boxes to impute missing borough names for records with geolocation information (via set operations) as a way to prevent over 85,000 requests. I trashed the box ‘solution’ once I found out about the official territorial boundaries (shapefiles). Yet, in the intervening time I had checked several services for speed and limits and I found that some geocoders were not returning the same geolocation or bounding boxes for the same query, so I investigated!
To date, April 2019, Geopy has 21 traditional geocoders (excluding What3Words), so I picked only four of them. Following are the links to the geocoders documentation and their respective service providers via Geopy:
- Nominatim: OpenStreetMaps
- GoogleV3: Google Map & Places API
- ArcGis: ESRI ArcGIS API
- AzureMaps: Microsoft Azure Maps API
Shapefile sources:
I used two shapefiles: that of New York City (with water extent), and that of Boston, without water extent as it was the only one I found.
- New York City: https://data.cityofnewyork.us/City-Government/Borough-Boundaries-Water-Areas-Included-/tv64-9x69
- Boston: https://data.boston.gov/dataset/city-of-boston-boundary2
Places queried:
- “New York City, NY, USA”
- “Cleopatra’s needle, Central Park, New York, NY, USA”
- “Bronx county, NY, USA”
- “Kings county, NY, USA”
- “New York county, NY, USA”
- “Queens county, NY, USA”
- “Richmond county, NY, USA”
- “Boston, MA, USA”
Update: Report on temporal differences:
Because I noticed that the results from this April were different from those from last September (2018), I put together an HTML report highlighting the differences. A persistent oddity is that half of the geocoders tested cannot distinguish between “New York City” and “New York county” (Manhattan): GoogleV3 and ArcGis return identical bounding boxes.
I’ve implemented the report by modifying a CSS slider designed by GH user drygiel.Thank you, drygiel!
Report of the older vs. newer geocoding results
In my GitHub repo, the Procedures notebook details the processing steps and the production of tables and maps included in the slider report.
The main conclusion from this comparison:
I presume that it is very unlikely that an application would use different geolocating services, but in the case some ‘hedging’ is involved (e.g. on limits, time-outs), the geolocation for the same query will be different. Additionally, my non-exhaustive comparison of four Geopy geocoders (out of 21), reveals that the boxing of a location is not always principled. For instance, Nominatim and GoogleV3 most often use the shapefile with water extent for boxing, whereas ArcGis and AzureMaps do not; moreover, ArcGis boxes typically extend further North than warranted by the existing shapefiles by at most 10 miles.
