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Querying Features

Feature collections can be queried to provide sets of features, or to return a single feature.

Query features

The path /collections/{collid}/items is the basic query to return a set of features from a feature collection. The response is a GeoJSON feature collection containing the result.

Example

http://localhost:9000/collections/ne.countries/items

Additional query parameters can be appended to the basic query to provide control over what sets of features are returned.

These are similar to using SQL statement clauses to control the results of a query. In fact, the service implements these parameters by generating the equivalent SQL. This allows the Postgres SQL engine to optimize the query execution plan.

Filter by bounding box

The query parameter bbox=MINX,MINY,MAXX,MAXY limits the features returned to those that intersect a specified bounding box. The bounding box is specified in geographic coordinates (longitude/latitude, SRID = 4326). If the source data has a non-geographic coordinate system, the bounding box is transformed to the source coordinate system to perform the query.

Example

http://localhost:9000/collections/ne.countries/items?bbox=10.4,43.3,26.4,47.7

Filter by properties

The response feature set can be filtered to include only features which have a given value for one or more properties. This is done by including query parameters which have the same name as the property to be filtered. The value of the parameter is the desired property value.

Example

http://localhost:9000/collections/ne.countries/items?continent=Europe

Specify respones properties

The query parameter properties=PROP1,PROP2,PROP3... specifies the feature properties returned in the response. This can reduce the response size of feature collections which have a large number of properties.

Example

http://localhost:9000/collections/ne.countries/items?properties=name,abbrev,pop_est

Limiting and paging

The query parameter limit=N controls the maximum number of features returned in a response document. There is also a server-defined maximum which cannot be exceeded.

The query parameter offset=N specifies the offset in the actual query result at which the response feature set starts.

When used together, these two parameters allow paging through large result sets.

Example

http://localhost:9000/collections/ne.countries/items?limit=50&offset=200

Even if the limit parameter is not specified, the response feature count is limited to avoid overloading the server and client. The default number of features in a response is set by the configuration parameter LimitDefault. The maximum number of features which can be requested in the limit parameter is set by the configuration parameters LimitMax.

Ordering

The result set can be ordered by any property it contains. This allows performing “greatest N” or “smallest N” queries.

  • orderBy=PROP orders results by PROP in ascending order

The sort order can be specified by appending :A (ascending) or :D (descending) to the ordering property name. The default is ascending order.

  • orderBy=PROP:A orders results by PROP in ascending order
  • orderBy=PROP:D orders results by PROP in descending order

Example

http://localhost:9000/collections/ne.countries/items?orderBy=name

Query a single feature

The path /collections/{collid}/items/{fid} allows querying a single feature in a feature collection by specifying its ID.

The response is a GeoJSON feature containing the result.

Example

http://localhost:9000/collections/ne.countries/items/23

Restrict properties

The query parameter properties=PROP1,PROP2,PROP3... restricts the properties which are returned in the response.

Example

http://localhost:9000/collections/ne.countries/items/23?properties=name,abbrev,pop_est