# The geology overlay

> Add depth-matched geological descriptions alongside your sample and test records.

When you are looking at samples or in-situ tests, it is often useful to see the
**geological description** for the depth each record sits at. The **geology
overlay** adds that context inline, without you opening the description table.

## When it is available

The **Geology** button appears in the toolbar only when the configuration has a
description table that Insight recognises, matched to the table you are viewing.
If you do not see the button, the current table has no geological descriptions to
overlay.

## Turning it on

Click **Geology** in the toolbar. Insight adds the description columns to the
grid, highlighted so they stand out from the table's own columns. Click it again
to remove them.

## Source codes

Insight recognises two AGS description sources:

| Code | Description |
| --- | --- |
| **GEOL** | Field Geological Descriptions. |
| **DLOG** | Driller Geological Description. |

When both are present in your data, a selector appears next to the button so you
can choose which source to overlay. When only one is present, Insight uses it
automatically.

## How records are matched

For each row, Insight works out the depth the record sits at and the location it
belongs to, then pulls the description whose depth range contains that depth at
that location. In other words, each sample or test shows the stratum it falls
within - not every description for the borehole.

<Callout type="note" title="Descriptions are read-only too">
  The overlay shows description data alongside your records; like everything in
  Insight, it is read-only. The descriptions themselves are captured in
  [Log](https://www.gimlabs.io/platform/log) and refined in
  [Manage](https://www.gimlabs.io/platform/manage).
</Callout>