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Bikeshare stations within a San Francisco buffer

In this example we are going to showcase how easily we can compute buffers around geometries using the Analytics Toolbox.

Creating a buffer of a neighborhood

The following query creates a buffer with a radius of 50 meters around San Francisco’s Financial District neighborhood using the ST_BUFFER function. The number of steps could be modified in order to make the lines smoother if needed.

SELECT `carto-un`.carto.ST_BUFFER(neighborhood_geom, 50, 'meters', 5) AS geo FROM `bigquery-public-data`.san_francisco_neighborhoods.boundaries WHERE neighborhood = "Financial District";

In this visualization you can see the Financial Disctrict (darker blue) and its buffer around it. Notice that buffers radius are not necesarily positive numbers. Negative numbers would generate a buffer in the interior of the district’s geomery.

Bikeshare stations within a buffer

Now let’s use the buffer as a way of defining a bigger region around the Financial District of San Francisco and filtering some other geometries.

SELECT ST_GEOGPOINT(d2.longitude,d2.latitude) AS geo FROM `bigquery-public-data`.san_francisco_neighborhoods.boundaries d1,
`bigquery-public-data`.san_francisco.bikeshare_stations d2
WHERE d1.neighborhood = "Financial District" AND ST_CONTAINS(`carto-un`.carto.ST_BUFFER(d1.neighborhood_geom, 50, 'meters', 5), ST_GEOGPOINT(d2.longitude, d2.latitude));

This query uses the ST_BUFFER and ST_CONTAINS functions in order to filter those bikeshare stations that are contained inside the buffered geometry. The result is displayed below, where bikeshare stations are represented as yellow dots.