dataservices-api/doc/isoline_functions.md

Isoline Functions

Isolines are contoured lines that display calculated levels over a given surface area. This enables you to view polygon dimensions by forward or reverse measurements. Isoline functions are calculated as the intersection of areas from the origin point, measured by distance (isodistance) or time (isochrone). For example, the distance of a road from a sidewalk. Isoline functions through CartoDB are available by requesting a single function in the Data Services API.

This service is subject to quota limitations, and extra fees may apply. View the Quota Information section for details, and recommendations, about to quota consumption.

You can use the isoline functions to retrieve, for example, isochrone lines from a certain location, specifying the mode and the ranges that will define each of the isolines. The following query calculates isolines for areas that are 5, 10 and 15 minutes (300, 600 and 900 seconds, respectively) away from the location by following a path defined by car routing. polygon({country_column})&api_key={api_key}

https://{username}.cartodb.com/api/v2/sql?q=SELECT cdb_isochrone('POINT(-3.70568 40.42028)'::geometry, 'car', ARRAY[300,600,900]::integer[])&api_key={api_key}

Notice that you can make use of Postgres or PostGIS functions in your Data Services API requests, as the result is a geometry that can be handled by the system. For example, suppose you need to retrieve the centroid of a specific country, you can wrap the resulting geometry from the geocoder functions inside the PostGIS ST_Centroid function:

https://{username}.cartodb.com/api/v2/sql?q=SELECT ST_Centroid(cdb_geocode_admin0_polygon('USA'))&api_key={api_key}

The following functions provide an isoline generator service, based on time or distance. This service uses the isolines service defined for your account. The default service limits the usage of displayed polygons represented on top of HERE maps.

cdb_isodistance(source geometry, mode text, range integer[], [options text[]])

Arguments

Name	Type	Description	Accepted values
source	geometry	Source point, in 4326 projection, which defines the start location.
mode	text	Type of transport used to calculate the isolines.	car or walk
range	integer[]	Range of the isoline, in meters.
options	text[]	(Optional) Multiple options to add more capabilities to the analysis. See Optional isolines parameters for details.

Returns

Name	Type	Description
center	geometry	Source point, in 4326 projection, which defines the start location.
data_range	integer	The range that belongs to the generated isoline.
the_geom	geometry(MultiPolygon)	MultiPolygon geometry of the generated isoline in the 4326 projection.

Examples

Select the results of the isodistance function

SELECT * FROM cdb_isodistance('POINT(-3.70568 40.42028)'::geometry, 'car', ARRAY[1000,2000]::integer[]);

SELECT * FROM cdb_isodistance('POINT(-3.70568 40.42028)'::geometry, 'walk', ARRAY[1000]::integer[], ARRAY['mode_traffic=enabled','quality=3']::text[]);

Select the geometric results of the isodistance function

SELECT the_geom FROM cdb_isodistance('POINT(-3.70568 40.42028)'::geometry, 'walk', ARRAY[1000]::integer[]);

Calculate and insert the generated isolines from points_table table to another table

INSERT INTO {table} (the_geom) SELECT (cdb_isodistance(the_geom, 'walk', string_to_array(distance, ',')::integer[])).the_geom FROM {points_table}

cdb_isochrone(source geometry, mode text, range integer[], [options text[]])

Arguments

This function uses the same parameters and information as the cdb_isodistance function, with the exception that the range is measured in seconds instead of meters.

Name	Type	Description	Accepted values
source	geometry	Source point, in 4326 projection, which defines the start location.
mode	text	Type of transport used to calculate the isolines.	car or walk
range	integer[]	Range of the isoline, in seconds.
options	text[]	(Optional) Multiple options to add more capabilities to the analysis. See Optional isolines parameters for details.

Examples

Select the results of the isochrone function

SELECT * FROM cdb_isochrone('POINT(-3.70568 40.42028)'::geometry, 'car', ARRAY[300,900,12000]::integer[]);

SELECT * FROM cdb_isochrone('POINT(-3.70568 40.42028)'::geometry, 'walk', ARRAY[300,900]::integer[], ARRAY['mode_traffic=enabled','quality=3']::text[]);

Select the geometric results of the isochrone function

SELECT the_geom FROM cdb_isochrone('POINT(-3.70568 40.42028)'::geometry, 'walk', ARRAY[300]::integer[]);

Calculate and insert the generated isolines from points_table table to another table

INSERT INTO {table} (the_geom) SELECT (cdb_isochrone(the_geom, 'walk', string_to_array(time_distance, ',')::integer[])).the_geom FROM {points_table}

Optional isoline parameters

The optional value parameters must be passed using the format: option=value.

Name	Type	Description	Accepted values
is_destination	boolean	If true, the source point is the destination instead of the starting location	true or false. false by default
mode_type	text	Type of route calculation	shortest or fastest. shortest by default
mode_traffic	text	Use traffic data to calculate the route	enabled or disabled. disabled by default
resolution	text	Allows you to specify the level of detail needed for the isoline polygon. Unit is meters per pixel. Higher resolution may increase the response time of the service.
maxpoints	text	Allows you to limit the amount of points in the returned isoline. If the isoline consists of multiple components, the sum of points from all components is considered. Each component will have at least two points. It is possible that more points than specified could be returned, in case when 2 * number of components is higher than the maxpoints value itself. Increasing the number of maxpoints may increase the response time of the service.
quality	text	Allows you to reduce the quality of the isoline in favor of the response time.	1, 2, 3. Default value is 1, corresponding to the best quality option.