Move doc from wiki to repo, closes #85

2015-07-01 07:01:50 -07:00
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+Determine the spatial extent of a tile based on the tile's XYZ coordinate.
+
+#### Using the function
+
+Take a common tile with coordinates x=3, y=2, z=2,
+
+![2/3/2](https://viz2.cartodb.com/tiles/quantile_breaks/2/3/2.png)
+
+To determine its extent you would run,
+
+```sql
+SELECT CDB_XYZ_Extent(3,2,2)
+--- Returns a WKB polygon in Webmercator (SRID 3857)
+```
+
+#### Arguements
+
+CDB_XYZ_Extent(x,y,z)
+
+* **x** integer
+* **y** integer
+* **z** integer