# Cross-sections

> Draw a section line across the site and produce a scaled geological cross-section as a PDF.

A **cross-section** is a scaled drawing of the ground along a line across your
site. You draw the line on the map, GIMLabs works out which locations fall near
it, and each one is placed at its true distance along the line and its true
level, drawn from your own section log template.

Open **Sections** in the map's side panel to start.

## The line and its buffer

Draw the **section line** across the map. It can be a straight line or a series
of segments; the drawing runs along it from one end to the other.

Around the line sits a **buffer** - a distance either side, in metres, that
decides which locations are captured. A hole inside the buffer is projected onto
the line and drawn at that point; a hole outside it is ignored. Widen the buffer
to pull in more of the site, narrow it to keep the drawing to the holes that
genuinely sit on the line.

<Callout type="note" title="The corridor and the capture are not identical">
  The shaded corridor drawn on the map has **square ends**, cut straight across
  at each end of the line. Capture measures the distance to the nearest point on
  the line itself, which at the ends means the distance to the end point - so a
  hole just beyond the end of the line can be captured even though it sits
  outside the shaded corridor. If a hole appears on the drawing that you did not
  expect, this is usually why. Untick it under **Locations**.
</Callout>

**Chainage origin** sets the distance the line starts at. Leave it at `0` for a
line that starts at zero, or set it to carry on the chainage of a neighbouring
section.

## Which locations are drawn

**Locations** shows how many of the captured holes are included - `5/6` means one
has been left out. Open it to tick and untick individual holes.

Two reasons to exclude one: it is inside the buffer but not really on the line,
or it is so close to a neighbour that the two strips overlap. Excluding a hole
changes only the drawing - the location, its data and every other section are
untouched.

## Scales

A section has a **horizontal** and a **vertical** scale, each stated as the `N`
in `1:N`.

Leave either blank and it is set to **Fit** - the largest drawing that fits the
space available. Name a scale and the drawing is made at that scale instead,
which is how you pin a section to a round number like 1:100 or 1:250 for issue.

Giving the two axes different scales is **vertical exaggeration**, and is normal
on a section where the site is far wider than it is deep.

<Callout type="tip" title="Scales are reported as drawn">
  The scale printed on the sheet is the scale the drawing was actually made at,
  never rounded to a tidier number. If you ask for a scale finer than the page
  allows, the drawing is made at the finest scale that does fit and the sheet
  says so - so a scale rule laid on the paper always reads true.
</Callout>

## Extent

**Extent** decides how much of the captured ground is drawn, without changing
the line or which holes were captured:

- **Drawn from** and **Drawn to** crop the drawing to a stretch of chainage.
- **Top** and **Base** crop it to a range of level, in mAOD. Leave either on
  **Fit** to take it from the data.

Cropping is presentation only. Moving the line to crop a drawing would change
which holes it captures and therefore the geology on it, which is why the two
are kept apart.

## Hatching

**Hatching** decides how the geology bands are filled:

- **Main soil type only** groups each band by its main soil type, so every
  variety of clay is drawn as `CLAY` with one hatch and one key entry. This is
  the default and it is what keeps the key readable.
- **Full geology code** draws every code exactly as logged, so `Sandy gravelly
  CLAY` gets its own hatch and its own key entry.

Both draw from your configuration's geology legend, so a section matches the
logs beside it. See
[the geology legend](/product-os/configurations/lists-units-and-assets#the-geology-legend)
for how patterns, colour fills and main types are set up.

## Producing the PDF

Pick the **Section** sheet - the page the drawing is placed on - and the
**Section log** - how each hole is drawn as a strip. Both come from
[Template](/template/logs-and-plans#sections-and-section-logs), and every
configuration ships with a standard set.

Generate, and you get a PDF at the scales stated on it.

## One line, many drawings

A saved section line is an **alignment**, not a drawing. You can produce several
sections from the same line - one at 1:100 for the report and another at 1:20
for a detail, or the same line cropped to different stretches of chainage - and
they all keep the one set of geometry. Move the line and every drawing of it
follows, rather than the copies quietly drifting apart.

## Schematic sections

A **schematic** is not a scaled section. There is no line and no projection:
you pick the holes, set the order they appear in and the spacing between them,
and they are drawn side by side. Use one to compare logs where the true
geography is not the point.

<Callout type="warning" title="Empty bands usually mean the legend, not the section">
  If the geology draws as blank boxes, the section is doing its job and the
  configuration's legend has no hatch patterns set. That is set up once in
  Product OS, not per section.
</Callout>