# Linewidth is added to the length of a line

### Question

When I draw a line segment in matplotlib the linewidth seems to be added to the length of the line. Below my code (not the most pythonic code, but it should do the trick). Am I doing something wrong or is this just a feature of matplotlib?

``````import matplotlib.pyplot as plt
import numpy as np

L1 = 100
L2 = 75
L3 = 100
Y = 3
N = 5
l_prev = 0
for l, c in zip(np.linspace(0, L1, N), range(N)):
plt.plot([l_prev, l], [0, 0], 'r', linewidth=20)
l_prev = l
l_prev = L1
for l, c in zip(np.linspace(L1, L1 + L2, N), range(N)):
plt.plot([l_prev, l], [Y, Y], 'g', linewidth=1)
l_prev = l
l_prev = L1
for l, c in zip(np.linspace(L1, L1 + L3, N), range(N)):
p = plt.plot([l_prev, l], [-Y, -Y], 'b', linewidth=10)
l_prev = l
plt.axvspan(xmin=L1, xmax=L1)
plt.axis([-5, 205, -5, 5])
plt.show()
``````

What I expected to see is three line segments: `[0,L1], [L1,L2] and [L1,L3]`. But the first line `[0,L1]` extends to `L1` + 'the diameter'....

1
24
9/26/2018 2:46:20 PM

It looks like the default `solid_capstyle` is `projecting`, which isn't the one you want:

``````plt.figure()
plt.plot([0, 100], [5, 5], linewidth=50, linestyle="-", c="blue",
solid_capstyle="butt")
plt.plot([0, 100], [15, 15], linewidth=50, linestyle="-", c="red",
solid_capstyle="round")
plt.plot([0, 100], [25, 25], linewidth=50, linestyle="-", c="purple",
solid_capstyle="projecting")
plt.axvline(x=100, c="black")
plt.xlim(0, 125)
plt.ylim(0, 30)
plt.savefig("cap.png")
`````` 56
4/28/2012 5:10:09 AM