# How to Change Intersection Point of X and Y Axis in Matplotlib

··404 words·2 mins·

In this post, I will share how to position the intersection of x and y axis at a specific point using Matplotlib.

# The spines#

In order to re-position x and y axis, we need to understand an important concept in Matplotlib — spines. According to Matplotlib documentation:

Spines are the lines connecting the axis tick marks and noting the boundaries of the data area. They can be placed at arbitrary positions. See function:set_position for more information.

In normal plot, we can clearly see four spines around the plot. Like the following plot:

Two of the 4 spines, i.e., bottom and left spines are used as x and y axis. Another two spines are used to indicate data boundary.

# Move the spines#

In order to move a specific spine, we use the set_position() method of spines. This method accepts a 2-tuple as its parameter. The first element of the tuple is used to indicate the desired coordinate system1, i.e., `axes` or `data`. If you use `axes`, the value for the second element is in the range \$[0.0, 1.0]\$. If you choose `data`, the value for the second element is the range of actual data range.

We can use `ax.spines` to get the four spines. The returned object will be a dict, whose keys are `bottom`, `left`, `top`, `right`. Then we use one of these keys to access a specific spine and customize it.

## Position spines in data coordinate#

Let us take a concrete example. Suppose we want to put the intersection of x and y axis at data coordinate \$(0, 0)\$, we can use the following snippet:

``````ax.spines['left'].set_position(('data', 0))
ax.spines['bottom'].set_position(('data', 0))
``````

The produced image will be:

The image looks a bit ugly since top and right spines now seem redundant. How do we remove them? It is easy:

``````ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
``````

Now the image will be prettier:

You can move the spines to whatever position you want, see more example below:

## Position spines in axes coordinate#

We can also position spines using the axes coordinate system. For example, if you want to place the x and y axis in the top right of the axes, i.e., in the axes coordinate \$(1, 1)\$, use the following script:

``````ax.spines['left'].set_position(('axes', 1))
ax.spines['bottom'].set_position(('axes', 1))
``````

The produced plot is

# References#

1. If you are not familiar with coordinate system in Matplotlib, you can check this tutorial↩︎

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