added geo.s2CellIDToken function, resolves #817

content/v2.0/reference/flux/stdlib/experimental/geo/s2cellidtoken.md

@@ -0,0 +1,81 @@
+---
+title: geo.s2CellIDToken() function
+description: >
+  The `geo.s2CellIDToken()` function returns an S2 cell ID token.
+menu:
+  v2_0_ref:
+    name: geo.s2CellIDToken
+    parent: Geo
+weight: 401
+v2.0/tags: [functions, geo]
+---
+
+The `geo.s2CellIDToken()` function returns an S2 cell ID token.
+
+_**Function type:** Transformation_
+
+```js
+import "experimental/geo"
+
+geo.s2CellIDToken(
+  point: {lat: 37.7858229, lon: -122.4058124},
+  level: 10
+)
+```
+
+## Parameters
+
+{{% note %}}
+`point` and `token` are mutually exclusive.
+{{% /note %}}
+
+### point
+Longitude and latitude in **decimal degrees** (WGS 84).
+
+_**Data type:** Object_
+
+### token
+S2 cell ID token to update.
+Useful for changing the S2 cell level of an existing S2 cell ID token.
+
+_**Data type:** String_
+
+### level
+[S2 Cell level](https://s2geometry.io/resources/s2cell_statistics.html) to use
+when generating the S2 cell ID token.
+
+_**Data type:** Integer_
+
+## Examples
+
+##### Use latitude and longitude values to generate S2 cell ID tokens
+```js
+import "experimental/geo"
+
+from(bucket: "example-bucket")
+  |> range(start: -1h)
+  |> filter(fn: (r) => r._measurement == "example-measurement")
+  |> map(fn: (r) => ({
+    r with
+    s2_cell_id: geo.s2CellIDToken(
+      point: {lat: r.lat, lon: r.lon},
+      level: 10
+    )})
+  )
+```
+
+##### Update S2 cell ID tokens using a new S2 cell level
+```js
+import "experimental/geo"
+
+from(bucket: "example-bucket")
+  |> range(start: -1h)
+  |> filter(fn: (r) => r._measurement == "example-measurement")
+  |> map(fn: (r) => ({
+    r with
+    s2_cell_id: geo.s2CellIDToken(
+      token: r.s2_cell_id,
+      level: 10
+    )})
+  )
+```