9.6 KiB
Boundaries Functions
Use the following functions to retrieve Boundary data. Data ranges from small areas (e.g. US Census Block Groups) to large areas (e.g. Countries). You can access boundaries by point location lookup, bounding box lookup, direct ID access and several other methods described below.
OBS_GetBoundariesByGeometry(polygon geometry, geometry_id text)
The OBS_GetBoundariesByGeometry(geometry, geometry_id) method returns a set of boundary geometries that intersect a supplied geometry. This can be used to find all boundaries that are within or overlap a bounding box. You have the ability to choose whether to retrieve all boundaries that intersect your supplied bounding box or only those that fall entirely inside of your bounding box.
Arguments
| Name | Description |
|---|---|
| polygon | a bounding box or other WGS84 geometry |
| geometry_id | a string identifier for a boundary geometry |
| timespan (optional) | year(s) to request from ('NULL' (default) gives most recent) |
| overlap_type (optional) | one of 'intersects' (default), 'contains', or 'within'. |
Returns
A table with the following columns:
| Column Name | Description |
|---|---|
| the_geom | a boundary geometry (e.g., US Census tracts) |
| geom_ref | a string identifier for the geometry (e.g., the geoid of a US Census tract) |
Example
Get all Census Tracts in Lower Manhattan plus nearby areas within the supplied bounding box.
SELECT *
FROM OBS_GetBoundariesByGeometry(
ST_MakeEnvelope(-74.0251922607,40.6945658517,
-73.9651107788,40.7377626342,
4326),
'us.census.tiger.census_tract')
API Example
Retrieve all Census tracts contained in a bounding box around Denver, CO as a JSON response:
http://observatory.cartodb.com/api/v2/sql?q=SELECT * FROM OBS_GetBoundariesByGeometry(ST_MakeEnvelope(-105.4287704158,39.4600507935,-104.5089737248,40.0901569675,4326),'us.census.tiger.census_tract', NULL, 'contains')
OBS_GetPointsByGeometry(polygon geometry, geometry_id text)
The OBS_GetPointsByGeometry(polygon, geometry_id) method returns point geometries and their geographical identifiers that intersect (or are contained by) a bounding box polygon and lie on the surface of a boundary corresponding to the boundary with same geographical identifiers (e.g., a point that is on a census tract with the same geoid). This is a useful alternative to OBS_GetBoundariesByGeometry listed above because it returns much less data for each location.
Arguments
| Name | Description |
|---|---|
| polygon | a bounding box or other geometry |
| geometry_id | a string identifier for a boundary geometry |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
| overlap_type (optional) | one of 'intersects' (default), 'contains', or 'within'. |
Returns
A table with the following columns:
| Column Name | Description |
|---|---|
| the_geom | a point geometry on a boundary (e.g., a point that lies on a US Census tract) |
| geom_ref | a string identifier for the geometry (e.g., the geoid of a US Census tract) |
Example
Get all Census Tracts in Lower Manhattan plus nearby areas within the supplied bounding box.
SELECT *
FROM OBS_GetPointsByGeometry(
ST_MakeEnvelope(-74.0251922607,40.6945658517,
-73.9651107788,40.7377626342,
4326),
'us.census.tiger.census_tract')
API Example
Retrieve all Census tracts intersecting a bounding box around Denver, CO as a JSON response:
http://observatory.cartodb.com/api/v2/sql?q=SELECT * FROM OBS_GetPointsByGeometry(ST_MakeEnvelope(-105.4287704158,39.4600507935,-104.5089737248,40.0901569675,4326), 'us.census.tiger.census_tract', NULL ,'contains')
OBS_GetBoundary(point geometry, boundary_id text)
The OBS_GetBoundary(point, boundary_id) method returns a boundary geometry defined as overlapping the point geometry and from the desired boundary set (e.g. Census Tracts). See the Boundary ID glossary table below.
Arguments
| Name | Description |
|---|---|
| point_geometry | a WGS84 polygon geometry (the_geom) |
| boundary_id | a boundary identifier from the Boundary ID glossary table below |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
Returns
| Value | Description |
|---|---|
| geom | WKB geometry |
Example
Overwrite a point geometry with a boundary geometry that contains it in your table
UPDATE tablename
SET the_geom = OBS_GetBoundary(the_geom, 'us.census.tiger.block_group')
OBS_GetBoundaryId(point geometry, boundary_id text)
The OBS_GetBoundaryId(point, boundary_id) returns a unique geometry_id for the boundary geometry that contains a given point geometry. See the Boundary ID glossary table below. The method can be combined with OBS_GetBoundaryById(geometry_id) to create a point aggregation workflow.
Arguments
| Name | Description |
|---|---|
| point | a WGS84 point geometry (the_geom) |
| boundary_id | a boundary identifier from the Boundary ID glossary table below |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
Returns
| Value | Description |
|---|---|
| geometry_id | a string identifier of a geometry in the Boundaries |
Example
Write the geometry_id that contains the point geometry for every row as a new column in your table
UPDATE tablename
SET new_column_name = OBS_GetBoundaryId(the_geom, ' "us.census.tiger".block_group')
OBS_GetBoundaryById(geometry_id text, boundary_id text)
The OBS_GetBoundaryById(geometry_id, boundary_id) returns the boundary geometry for a unique geometry_id. A geometry_id can be found using the OBS_GetBoundaryId(point, boundary_id) method described above.
Arguments
| Name | Description |
|---|---|
| geometry_id | a string identifier for a Boundary geometry |
| boundary_id | a boundary identifier from the Boundary ID glossary table below |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
Returns
A JSON object containing the following properties
| Key | Description |
|---|---|
| geom | a WGS84 polygon geometry |
Example
Use a table of geometry_id to select the unique boundaries. Useful with the Create Dataset from Query option in CartoDB.
SELECT OBS_GetBoundaryById(geometry_id) As the_geom, geometry_id
FROM tablename
GROUP BY geometry_id
OBS_GetBoundariesByPointAndRadius(point geometry, radius numeric, boundary_id text)
The OBS_GetBoundariesByPointAndRadius(point, radius, boundary_id) method returns boundary geometries and their geographical identifiers that intersect (or are contained by) a circle centered on a point with a radius.
Arguments
| Name | Description |
|---|---|
| point | a WGS84 point geometry |
| radius | a radius (in meters) from the center point |
| geometry_id | a string identifier for a boundary geometry |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
| overlap_type (optional) | one of 'intersects' (default), 'contains', or 'within'. |
Returns
A table with the following columns:
| Column Name | Description |
|---|---|
| the_geom | a boundary geometry (e.g., a US Census tract) |
| geom_ref | a string identifier for the geometry (e.g., the geoid of a US Census tract) |
Example
Get Census tracts which intersect within 10 miles of Downtown, Colorado. In the Editor, you can simple use "Table from Query" to turn the result into a new dataset.
SELECT *
FROM OBS_GetBoundariesByPointAndRadius(
CDB_LatLng(39.7392, -104.9903), -- Denver, Colorado
10000 * 1.609, -- 10 miles (10km * conversion to miles)
'us.census.tiger.census_tract')
OBS_GetPointsByPointAndRadius(point geometry, radius numeric, boundary_id text)
The OBS_GetPointsByPointAndRadius(point, radius, boundary_id) method returns point geometries on boundaries (e.g., a point that lies on a Census tract) and their geographical identifiers that intersect (or are contained by) a circle centered on a point with a radius.
Arguments
| Name | Description |
|---|---|
| point | a WGS84 point geometry |
| radius | radius (in meters) |
| geometry_id | a string identifier for a boundary geometry |
| timespan (optional) | year(s) to request from (NULL (default) gives most recent) |
| overlap_type (optional) | one of 'intersects' (default), 'contains', or 'within'. |
Returns
A table with the following columns:
| Column Name | Description |
|---|---|
| the_geom | a point geometry (e.g., a point on a US Census tract) |
| geom_ref | a string identifier for the geometry (e.g., the geoid of a US Census tract) |
Example
Get Census tracts which intersect within 10 miles of Downtown, Colorado. In the Editor, you can simple use "Table from Query" to turn the result into a new dataset.
SELECT *
FROM OBS_GetPointsByPointAndRadius(
CDB_LatLng(39.7392, -104.9903), -- Denver, Colorado
10000 * 1.609, -- 10 miles (10km * conversion to miles)
'us.census.tiger.census_tract')