## What is the Universal Pollen Index (UPI)?

The Universal Pollen Index (UPI) is designed to offer a globally unified scale
for comparing pollen levels across different areas. The index helps assess the
risk of pollen exposure based on various factors for people allergic or
sensitive to pollen. Based on a multilayer model, it is a representation of
pollen level data that considers the concentration per plant model, many
different local pollen indices (LPI) used worldwide, and the allergenicity of
different plant pollen types to predict the number of pollen grains per cubic
meter (grains/m3) per day.

The heatmapTiles endpoint returns heatmap tiles that can be overlaid
on a basemap. Heatmap tiles display the UPI across the globe for a given plant
type (`TREE`, `GRASS`, or `WEED`).

The index consists of six categories:

| Value | Color | Description |
|---|---|---|
| 0 | ![Gray color swatch for none](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | None |
| 1 | ![Dark green color swatch for very low](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | Very Low |
| 2 | ![Light green color swatch for low](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | Low |
| 3 | ![Yellow color swatch for moderate](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | Moderate |
| 4 | ![Orange color swatch for high](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | High |
| 5 | ![Red color swatch for very high](https://fonts.gstatic.com/s/i/short-term/release/googlesymbols/square/fill1/24px.svg) | Very High |

Each category is based on specific concentration levels of pollen in a
particular area and their effect on the severity of allergic symptoms that are
usually experienced, providing a comprehensive representation of pollen levels.
By integrating the UPI, users can compare and assess pollen conditions in
various locations.

For example, the following heatmap tile shows `TREE` pollen levels ranging from
**Very Low** to **Very High**:

![An example of a heatmap tile using the TREE_UPI map.](https://developers.google.com/static/maps/images/pollen-heatmap-example.png)

## Supported plants

The Pollen API supports 3 different types of plants: **Grass** , **Weed** ,
and **Tree**. Because a plant's availability is subject to actual data source
measurements and reports, Pollen API plant data may vary across locations.

The following list shows supported plant codes and their metadata:

| Plant Code | Display Name | Type |
| `ALDER` | Alder | Tree |
| `ASH` | Ash | Tree |
| `BIRCH` | Birch | Tree |
| `COTTONWOOD` | Cottonwood | Tree |
| `ELM` | Elm | Tree |
| `MAPLE` | Maple | Tree |
| `OLIVE` | Olive | Tree |
| `JUNIPER` | Juniper | Tree |
| `OAK` | Oak | Tree |
| `PINE` | Pine | Tree |
| `CYPRESS_PINE` | Cypress pine | Tree |
| `HAZEL` | Hazel | Tree |
| `GRAMINALES` | Grasses | Grass |
| `JAPANESE_CEDAR` | Japanese cedar | Tree |
| `JAPANESE_CYPRESS` | Japanese cypress | Tree |
| `RAGWEED` | Ragweed | Weed |
| `MUGWORT` | Mugwort | Weed |
|---|---|---|