Circos > Documentation > Tutorials > Quick Start > Selection And Scale
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1 — Quick Start

3. Ideogram Selection, Scale, Color & Orientation

In this section, we will adjust which chromosomes are drawn and change their scale, color and orientation.

Getting the ideogram layout right is important. For example, making all chromosomes appear to be the same size can emphasize the comparison between relative positions in patterns.

ideogram selection

The default behaviour is to display all chromosomes defined in the karyotype file, in order of appearance.

To select a subset of chromosomes, set chromosomes_display_default=no

chromosomes_display_default = no

and then use the chromosomes parameter to provide either a list

chromosomes                 = hs1;hs2;hs3;h4

or regular expression in

chromosomes                 = /hs[1-4]$/

to specify which chromosomes to show. You can combine these methods

chromosomes                 = /hs[1-4]$/;hs10;hs11

and use - prefix to specify that you don't want a chromosome to be drawn

chromosomes                 = /hs[1-4]$/;-hs3

Note that the list uses ; as the delimiter. The reason why , is not used is because the chromosome entry can include a list of chromosome regions to draw, such as

chromosomes                 = hs1:(-100,120-);hs2;hs3;h4

The regular expression can match a partial string, so don't forget to include a trailing $ anchor if you don't mean to match hs10,hs11,...

ideogram scale

The size of the ideogram on the figure can be adjusted using an absolute or relative magnification.

Absolute scale applies a fixed magnification to an ideogram

# hs1 0.25x zoom
# hs2 2.00x zoom
chromosomes_scale   = hs1=0.25,hs2=2.0

Relative scale defines the size of the ideogram relative to image circumference

# hs1 25% of figure
# hs2 50% of figure
chromosomes_scale   = hs1=0.25r,hs2=0.50r

Normalized relative scale distributes several ideograms evenly within a fraction of the figure.

# hs1,hs2 distributed evenly within 50% of figure (each is 25%)
chromosomes_scale   = /hs[12]/=0.5rn

A useful idiom is to select all ideograms and distribute them across entire figure.

# all ideograms distributed evenly within entire figure
chromosomes_scale   = /./=1rn

scale progression

By default, the scale progression is clockwise. You can set the global angle progression using angle_orientation in the <image> block

# The * suffix is used to overwrite a parameter. In this case, the 
# angle_orientation imported from etc/image is assigned a different value.
angle_orientation* = counterclockwise
<<include etc/image>>

To reverse it for one or several ideograms, use chromosomes-reverse

chromosomes_reverse = /hs[234]/

In this case the regular expression did not require a trailing $ because it applies only to those chromosomes that are displayed. Thus, even though /hs[234]/ does match hs20, it does not matter because this chromosome is not shown.

ideogram color

The color of each ideogram is taken from the karyotype file. To change it, use chromosomes_color

chromosomes_color   = hs1=red,hs2=orange,hs3=green,hs4=blue

ideogram radial position

By default, all ideograms are placed at the same radial position, as defined by the radius parameter in the <ideogram> block. You can selectively move one or more of the ideograms radially by definining a new radial position using chromosomes_radius.

Probably the most convenient way to do this is to use relative coordinates (r suffix), which are interpreted relative to the default ideogram radius. For example,

chromosomes_radius  = hs4:0.9r

would place chromosome 4 at 0.9x the radius of all other chromosomes.