It's Autumn! Prices fall like leaves! - hours only!Up to 80% off on all courses and bundles.-Close
Introduction
Functions returning geometries
Collections
13. ST_Area
Summary

## Instruction

Fine! You know that ST_Area returns the area of the polygon, but what happens if we use it with a collection? The answer is: it will return the total area of all polygons in the collection. For instance:

Well done! Now, you know that the ST_Area function returns the area of a polygon, but what happens if we pass in a collection to this function? Simply put, it calculates the total area of all polygons in the collection! This simplifies matters quite a bit, eliminating the need to call an aggregate function like SUM if you already have a collection on hand. For instance:

SELECT
id,
ST_Area(ST_Transform(geo_data,26910))
FROM sf_chains;

For each collection, the query above will show its id and the total area of all polygons it contains.

## Exercise

What is the total area of all Tranquil Jewel Hotels in San Francisco (collection with id = 1)? Provide the answer in square meters.

### Stuck? Here's a hint!

Remember to use ST_Tranform with an SRID of 26910 before you calculate ST_Area. 