7.7 KiB
Reverse geocoding
Reverse geocoding is used for finding places or addresses near a latitude, longitude pair—like clicking on a map to see what's there when the map doesn't show it otherwise. For example, picture a map showing building outlines but no labels, then clicking on a building and being shown the name of the business. That's reverse geocoding.
With reverse geocoding with Mapzen Search, you can look up all sorts of information about points on a map, including:
- addresses
- points of interest (businesses, museums, parks, and so on)
- neighborhoods
- cities
- states
- postal areas
- countries
To get started with reverse geocoding, you need a developer API key and a latitude, longitude pair in decimal degrees specified with the parameters point.lat and point.lon, respectively. For example, the Eiffel Tower in Paris, France, is located at 48.858268,2.294471. The reverse geocode query for this would be:
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=48.858268&point.lon=2.294471
Notice that the first result is the Eiffel Tower (well, Tour Eiffel). The output is the standard GeoJSON format.
Reverse geocoding parameters
Like other queries with Mapzen Search, reverse geocoding has optional, additional parameters you can use to refine results.
| Parameter | Type | Required | Default | Example |
|---|---|---|---|---|
api_key |
string | yes | none | get yours here! |
point.lat |
floating point number | yes | none | 48.858268 |
point.lon |
floating point number | yes | none | 2.294471 |
size |
integer | no | 10 |
3 |
layers |
comma-delimited string array | no | none (all layers) | address,locality |
sources |
comma-delimited string array | no | none (all sources) | oa,gn |
boundary.country |
ISO-3166 alpha-2 or alpha-3 | no | none | FR |
Size
A basic parameter for filtering is size, which is used to limit the number of results returned. In the earlier request that returned the Eiffel Tower (or 'Tour Eiffel', to be exact), notice that other results were returned including "Bureau de Gustave Eiffel" (a museum) and "Le Jules Verne" (a restaurant). To limit a reverse geocode to only the first result, pass the size parameter:
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=48.858268&point.lon=2.294471&size=1
The default value for size is 10 and the maximum value is 40. Specifying a value greater than 40 will override to 40 and return a warning in the response metadata.
Filter by data source
By default, reverse geocoding returns results from any data source available to Mapzen Search. To filter results by source, specify one or more valid source names in a comma-delimited list using the sources parameter. For example, the following request returns only results from OpenStreetMap:
| source | name | short name |
|---|---|---|
| OpenStreetMap | openstreetmap |
osm |
| OpenAddresses | openaddresses |
oa |
| Who's on First | whosonfirst |
wof |
| GeoNames | geonames |
gn |
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=48.858268&point.lon=2.294471&sources=osm
Filter by layers (data type)
Without specifying further, reverse geocoding doesn't restrict results to a particular type (street, venue, neighbourhood, and so on). If your application is only concerned with, say, which city a latitude, longitude is closest to, then use the layers parameter. For example, the following request returns only results that are localities (cities and towns):
| layer | description |
|---|---|
venue |
points of interest, businesses, things with walls |
address |
places with a street address |
street |
streets,roads,highways |
country |
places that issue passports, nations, nation-states |
macroregion |
a related group of regions. Mostly in Europe |
region |
states and provinces |
macrocounty |
a related group of counties. Mostly in Europe. |
county |
official governmental area; usually bigger than a locality, almost always smaller than a region |
locality |
towns, hamlets, cities |
localadmin |
local administrative boundaries |
borough |
a local administrative boundary, currently only used for New York City |
neighbourhood |
social communities, neighbourhoods |
coarse |
alias for simultaneously using all administrative layers (everything except venue and address) |
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=48.858268&point.lon=2.294471&layers=locality
Filter by country
If you are performing a reverse geocode near a country boundary, and are only interested in results from one country and not the other, you can specify a country code. You can set the boundary.country parameter value to the alpha-2 or alpha-3 ISO-3166 country code. For example, the latitude,longitude pair 47.270521,9.530846 is on the boundary of Austria, Liechtenstein, and Switzerland. Without specifying a boundary.country, the first 10 results returned may come from all three countries. By including boundary.country=LIE, all 10 results will be from Liechtenstein. Here's the request in action:
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=47.270521&point.lon=9.530846&boundary.country=LIE
Note that UK is not a valid ISO 3166-1 alpha-2 country code.
Distance Confidence scores for the results
Each result returned has a distance from the query point (in meters) and an associated confidence score. Confidence scores are calculated based on the distance from the result to the supplied point.lat and point.lon. Confidence scoring for reverse geocode results is likely to change with different data sources and layers.
Distance from point.lat/point.lon |
Confidence score |
|---|---|
| < 1m | 1.0 |
| < 10m | 0.9 |
| < 100m | 0.8 |
| < 250m | 0.7 |
| < 1km | 0.6 |
| >= 1km | 0.5 |
Example requests
This section shows how the various parameters can be combined to form complex use cases.
- All results near the Tower of London
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=51.5081124&point.lon=-0.0759493
- Only OpenStreetMap results near the Tower of London
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=51.5081124&point.lon=-0.0759493&sources=osm
- Only street addresses near the Tower of London
/v1/reverse?api_key=mapzen-xxxxxx&point.lat=51.5081124&point.lon=-0.0759493&layers=address
- Only OpenStreetMap street addresses near the Tower of London
- Only the first OpenStreetMap address near the Tower of London