[Data Observatory Measures](https://carto.com/docs/carto-engine/data/overview/#measures-methods) are the numerical location data you can access. The measure functions allow you to access individual measures to augment your own data or integrate in your analysis workflows. Measures are used by sending an identifier or a geometry (point or polygon) and receiving back a measure (an absolute value) for that location.
There are hundreds of measures and the list is growing with each release. You can currently discover and learn about measures contained in the Data Observatory by downloading our [Data Catalog](https://cartodb.github.io/bigmetadata/index.html).
You can [access](https://carto.com/docs/carto-engine/data/accessing) measures through CARTO Builder. The same methods will work if you are using the CARTO Engine to develop your application. We [encourage you](https://carto.com/docs/carto-engine/data/accessing/#best-practices) to use table modifying methods (UPDATE and INSERT) over dynamic methods (SELECT).
The ```OBS_GetUSCensusMeasure(point, measure_name)``` function returns a measure based on a subset of the US Census variables at a point location. The ```OBS_GetUSCensusMeasure``` function is limited to only a subset of all measures that are available in the Data Observatory. To access the full list, use measure IDs with the ```OBS_GetMeasure``` function below.
measure_name | a human-readable name of a US Census variable. The list of measure_names is [available in the Glossary](https://carto.com/docs/carto-engine/data/glossary/#obsgetuscensusmeasure-names-table).
normalize | for measures that are **sums** (e.g. population) the default normalization is 'area' and response comes back as a rate per square kilometer. Other options are 'denominator', which will use the denominator specified in the [Data Catalog](https://cartodb.github.io/bigmetadata/index.html) (optional)
The ```OBS_GetUSCensusMeasure(polygon, measure_name)``` function returns a measure based on a subset of the US Census variables within a given polygon. The ```OBS_GetUSCensusMeasure``` function is limited to only a subset of all measures that are available in the Data Observatory. To access the full list, use the ```OBS_GetMeasure``` function below.
measure_name | a human readable string name of a US Census variable. The list of measure_names is [available in the Glossary](https://carto.com/docs/carto-engine/data/glossary/#obsgetuscensusmeasure-names-table).
normalize | for measures that are **sums** (e.g. population) the default normalization is 'none' and response comes back as a raw value. Other options are 'denominator', which will use the denominator specified in the [Data Catalog](https://cartodb.github.io/bigmetadata/index.html) (optional)
The ```OBS_GetMeasure(point, measure_id)``` function returns any Data Observatory measure at a point location. You can browse all available Measures in the [Catalog](https://cartodb.github.io/bigmetadata/index.html).
measure_id | a measure identifier from the Data Observatory ([see available measures](https://cartodb.github.io/bigmetadata/observatory.pdf)). It is important to note that these are different than 'measure_name' used in the Census based functions above.
normalize | for measures that are **sums** (e.g. population) the default normalization is 'area' and response comes back as a rate per square kilometer. The other option is 'denominator', which will use the denominator specified in the [Data Catalog](https://cartodb.github.io/bigmetadata/index.html). (optional)
normalize | for measures that are **sums** (e.g. population) the default normalization is 'none' and response comes back as a raw value. Other options are 'denominator', which will use the denominator specified in the [Data Catalog](https://cartodb.github.io/bigmetadata/index.html) (optional)
The ```OBS_GetMeasureById(geom_ref, measure_id, boundary_id)``` function returns any Data Observatory measure that corresponds to the boundary in ```boundary_id``` that has a geometry reference of ```geom_ref```.
#### Arguments
Name |Description
--- | ---
geom_ref | a geometry reference (e.g., a US Census geoid)
value | the raw measure associated with `geom_ref`
#### Example
Add a measure to an empty column based on county geoids in your table
```SQL
UPDATE tablename
SET household_count = OBS_GetMeasureById(geoid_column, 'us.census.acs.B11001001', 'us.census.tiger.county')
```
#### Errors
* Returns `NULL` if there is a mismatch between the geometry reference and the boundary id such as using the geoid of a county with the boundary of block groups
The ```OBS_GetCategory(point, category_id)``` function returns any Data Observatory Category value at a point location. The Categories available are currently limited to Segmentation categories. See the Segmentation section of the [Catalog](https://cartodb.github.io/bigmetadata/index.html) for more detail.
metadata | A JSON array composed of metadata input objects. Each indicates one desired measure for an output column, and optionally additional parameters about that column
The schema of the metadata input objects are as follows:
Metadata Input Key | Description
--- | -----------
numer_id | The identifier for the desired measurement. If left blank, but a `geom_id` is specified, the column will return a geometry instead of a measurement.
geom_id | Identifier for a desired geographic boundary level to use when calculating measures. Will be automatically assigned if undefined. If defined but `numer_id` is blank, then the column will return a geometry instead of a measurement.
normalization | The desired normalization. One of 'area', 'prenormalized', or 'denominated'. 'Area' will normalize the measure per square kilometer, 'prenormalized' will return the original value, and 'denominated' will normalize by a denominator. Ignored if this metadata object specifies a geometry.
denom_id | Identifier for a desired normalization column in case `normalization` is 'denominated'. Will be automatically assigned if necessary. Ignored if this metadata object specifies a geometry.
numer_timespan | The desired timespan for the measurement. Defaults to most recent timespan available if left unspecified.
target_area | Instead of aiming to have `target_geoms` in the area of the geometry passed as `extent`, fill this area. Unit is square degrees WGS84. Set this to `0` if you want to use the smallest source geometry for this element of metadata, for example if you're passing in points.
target_geoms | Override global `target_geoms` for this element of metadata
The ```OBS_MetadataValidation``` function performs a validation check over the known issues using the extent, type of geometry, and metadata that is being used in the ```OBS_GetMeta``` function.
geometry_type | The geometry type of the source data
metadata | A JSON array composed of metadata input objects. Each indicates one desired measure for an output column, and optional additional parameters about that column
target_geoms | Target number of geometries. Boundaries with close to this many objects within `extent` will be ranked highest
numer_id | The identifier for the desired measurement. If left blank, a `geom_id` is specified and the column returns a geometry, instead of a measurement
geom_id | Identifier for a desired geographic boundary level used to calculate measures. If undefined, this is automatically assigned. If defined, `numer_id` is blank and the column returns a geometry, instead of a measurement
normalization | The desired normalization. One of 'area', 'prenormalized', or 'denominated'. 'Area' will normalize the measure per square kilometer, 'prenormalized' will return the original value, and 'denominated' will normalize by a denominator. If the metadata object specifies a geometry, this is ignored
denom_id | When `normalization` is 'denominated', this is the identifier for a desired normalization column. This is automatically assigned. If the metadata object specifies a geometry, this is ignored
numer_timespan | The desired timespan for the measurement. If left unspecified, it defaults to the most recent timespan available
geom_timespan | The desired timespan for the geometry. If left unspecified, it defaults to the timespan matching `numer_timespan`
target_area | Instead of aiming to have `target_geoms` in the area of the geometry passed as `extent`, fill this area. Unit is square degrees WGS84. Set this to `0` if you want to use the smallest source geometry for this element of metadata. For example, if you are passing in points
Validate metadata with two additional columns of US census data; using a boundary relevant for the geometry provided and the latest timespan. Limited to the most recent column, and the most relevant, based on the extent and density of input geometries in `tablename`.
The ```OBS_GetData(geomvals, metadata)``` function returns a measure and/or
geometry corresponding to the `metadata` JSON array for each every Geometry of
the `geomval` element in the `geomvals` array. The metadata argument must be
obtained from ```OBS_GetMeta(extent, metadata)```.
#### Arguments
Name | Description
---- | -----------
geomvals | An array of `geomval` elements, which are obtained by casting together a `Geometry` and a `Numeric`. This should be obtained by using `ARRAY_AGG((the_geom, cartodb_id)::geomval)` from the CARTO table one wishes to obtain data for.
metadata | A JSON array composed of metadata output objects from ```OBS_GetMeta(extent, metadata)```. The schema of the elements of the `metadata` JSON array corresponds to that of the output of ```OBS_GetMeta(extent, metadata)```, and this argument must be obtained from that function in order for the call to be valid.
A TABLE with the following schema, where each element of the input `geomvals`
array corresponds to one row:
Column | Type | Description
------ | ---- | -----------
id | Numeric | ID corresponding to the `val` component of an element of the input `geomvals` array
data | JSON | A JSON array with elements corresponding to the input `metadata` JSON array
Each `data` object has the following keys:
Key | Description
--- | -----------
value | The value of the measurement or geometry for the geometry corresponding to this row and measurement corresponding to this position in the `metadata` JSON array
To determine the appropriate cast for `value`, one can use the `numer_type`
or `geom_type` key corresponding to that value in the input `metadata` JSON
array.
#### Examples
Obtain population densities for every geometry in a table, keyed by cartodb_id:
metadata | A JSON array composed of metadata output objects from ```OBS_GetMeta(extent, metadata)```. The schema of the elements of the `metadata` JSON array corresponds to that of the output of ```OBS_GetMeta(extent, metadata)```, and this argument must be obtained from that function in order for the call to be valid.
A TABLE with the following schema, where each element of the input `ids` array
corresponds to one row:
Column | Type | Description
------ | ---- | -----------
id | Text | ID corresponding to an element of the input `ids` array
data | JSON | A JSON array with elements corresponding to the input `metadata` JSON array
Each `data` object has the following keys:
Key | Description
--- | -----------
value | The value of the measurement or geometry for the geometry corresponding to this row and measurement corresponding to this position in the `metadata` JSON array
To determine the appropriate cast for `value`, one can use the `numer_type`
or `geom_type` key corresponding to that value in the input `metadata` JSON
array.
#### Examples
Obtain population densities for every row of a table with FIPS code county IDs
