Circos > Documentation > Tutorials > Quick Start > Axes And Backgrounds
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Use the latest version of Circos and read Circos best practices—these list recent important changes and identify sources of common problems.
If you are having trouble, post your issue to the Circos Google Group and include all files and detailed error logs. Please do not email me directly unless it is urgent—you are much more likely to receive a timely reply from the group.
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1 — Quick Start

6. Axes & Backgrounds

A track's background can be colored using <backgrounds> block and graduated using <axes> block.

<plot>
...
# axes
<axes>
 <axis>
 ...
 </axis>
 <axis>
 ...
 </axis>
 ...
</axes>

# backgrounds
<backgrounds>
 <background>
 ...
 </background>
 <background>
 ...
 </background>
 ...
</backgrounds>

</plot>

axes

Much like ticks, axes are defined in groups. Each group can be spaced either with absolute or relative spacing. You can provide an axis line at specific positions and, for groups which have spacing, skip some positions.

  • spacing - absolute or relative spacing of the axis
  • position - fixed position (or positions) for axes
  • position_skip - fixed position (or positions) to skip when drawing axis lines
  • y0 - absolute or relative start of axis lines
  • y1 - absolute or relative start of axis lines
  • color - color of axis lines
  • thickness - thickness of axis lines
<axes>

# Show axes only on ideograms that have data for this track
show = data

thickness = 1
color     = lgrey

<axis>
spacing   = 0.1r
</axis>

<axis>
spacing   = 0.2r
color     = grey
</axis>

<axis>
position  = 0.5r
color     = red
</axis>

<axis>
position  = 0.85r
color     = green
thickness = 2
</axis>

</axes>

backgrounds

Background elements are color rings within the track boundary between y0 and y1 limits. Multiple background elements can e used to give the track a striped or gradated look. Each element is defined as a separate <background> block, which are processed in order of appearance.

If y0 and y1 limits are not specified, the boundaries of the track are used.

<backgrounds>

# Show the backgrounds only for ideograms that have data
show  = data

<background>
color = vvlgrey
</background>
<background>
color = vlgrey
# the "r" suffix indicates position relative to track data range
y0    = 0.2r
y1    = 0.5r
</background>
<background>
color = lgrey
y0    = 0.5r
y1    = 0.8r
</background>
<background>
color = grey
# if y1 is not specified, the plot maximum is used (e.g. y1=1r)
y0    = 0.8r
</background>

</backgrounds>

stand-alone axes and blackground <plot> blocks

In most cases, the purpose of a <plot> block is to show data. Axes and backgrounds associated with a <plot> block that contains data will always be drawn under the data.

To precisely control whether axes and backgrounds are placed below or over the data, use a bare <plot> block (one without file or type parameter). Doing so will use the <plot> block to draw the axes and background only, without any data.

<plot>

# no file or type parameter

r0 = 0.5r
r1 = 0.75r

# use z to determine whether this block (axes,background) will be
# drawn on top of other plot blocks. 

z  = 10

<axes>
 ...
</axes>

<backgrounds>
 ...
</backgrounds>

</plot>

Here is an example of how to use this kind of axes <plot> block. Depending on the z parameter of the axis <plot> block, the axes are drawn above or below the data in the second block. By setting the axis color to have transparency (grey_a3), the axes will blend with the histogram bins when drawn on top of then.


<plots>

# positions are inherited by both <plot> blocks

r0 = 0.5r
r1 = 0.8r

<plot>
 z = 10 # drawn on top of data
 # z = -10 # drawn below data
 <axes>
  <axis>
   spacing   = 0.1r
   color     = grey_a3
   thickness = 1
  </axis>
 </axes>
</plot>

<plot>
 # default z value is 0
 type = histogram
 file = data.txt
</plot>

</plots>